diff --git a/PowerEditor/src/Notepad_plus.cpp b/PowerEditor/src/Notepad_plus.cpp
index 16c09ddae..70e102089 100644
--- a/PowerEditor/src/Notepad_plus.cpp
+++ b/PowerEditor/src/Notepad_plus.cpp
@@ -638,9 +638,17 @@ LRESULT Notepad_plus::init(HWND hwnd)
 	::DrawMenuBar(hwnd);
 
 
-	//Windows menu
+	// Windows menu
 	_windowsMenu.init(_mainMenuHandle);
 
+	// if user set system codepage to UTF8, ANSI encoding capacity should be disable once for all
+	if (NppParameters::getInstance().isCurrentSystemCodepageUTF8())
+	{
+		enableCommand(IDM_FORMAT_ANSI, false, MENU);
+		enableCommand(IDM_FORMAT_CONV2_ANSI, false, MENU);
+	}
+
+
 	// Update Scintilla context menu strings (translated)
 	vector<MenuItemUnit> & tmp = nppParam.getContextMenuItems();
 	size_t len = tmp.size();
@@ -2510,7 +2518,7 @@ int Notepad_plus::doDeleteOrNot(const wchar_t *fn)
 
 void Notepad_plus::enableMenu(int cmdID, bool doEnable) const
 {
-	int flag = doEnable?MF_ENABLED | MF_BYCOMMAND:MF_DISABLED | MF_GRAYED | MF_BYCOMMAND;
+	int flag = doEnable ? MF_ENABLED | MF_BYCOMMAND : MF_GRAYED | MF_DISABLED | MF_BYCOMMAND;
 	::EnableMenuItem(_mainMenuHandle, cmdID, flag);
 }
 
@@ -2724,6 +2732,9 @@ void Notepad_plus::setupColorSampleBitmapsOnMainMenuItems()
 	}
 }
 
+// doCheck searches for the menu item matching the provided id across the main menu and all of its submenus,
+// once the target id is found, it ensures that item is checked, and all other menu items at that same level are automatically unchecked.
+// If id is -1, then all the menu items are unchecked.
 bool doCheck(HMENU mainHandle, int id)
 {
 	MENUITEMINFO mii{};
@@ -2735,7 +2746,7 @@ bool doCheck(HMENU mainHandle, int id)
 	for (int i = 0; i < count; i++)
 	{
 		::GetMenuItemInfo(mainHandle, i, MF_BYPOSITION, &mii);
-		if (mii.fType == MFT_RADIOCHECK || mii.fType == MFT_STRING)
+		if (!(mii.fState & MFS_GRAYED) && (mii.fType == MFT_RADIOCHECK || mii.fType == MFT_STRING))
 		{
 			bool checked = mii.hSubMenu ? doCheck(mii.hSubMenu, id) : (mii.wID == (unsigned int)id);
 			if (checked)
@@ -3072,7 +3083,7 @@ void Notepad_plus::setUniModeText()
 				uniModeTextString = L"UTF-16 Big Endian"; break;
 			case uni16LE_NoBOM:
 				uniModeTextString = L"UTF-16 Little Endian"; break;
-			case uniCookie:
+			case uniUTF8_NoBOM:
 				uniModeTextString = L"UTF-8"; break;
 			default :
 				uniModeTextString = L"ANSI";
@@ -4191,7 +4202,7 @@ size_t Notepad_plus::getSelectedCharNumber(UniMode u)
 {
 	size_t result = 0;
 	size_t numSel = _pEditView->execute(SCI_GETSELECTIONS);
-	if (u == uniUTF8 || u == uniCookie)
+	if (u == uniUTF8 || u == uniUTF8_NoBOM)
 	{
 		for (size_t i = 0; i < numSel; ++i)
 		{
@@ -4254,7 +4265,7 @@ static inline size_t countUtf8Characters(const unsigned char *buf, size_t pos, s
 
 size_t Notepad_plus::getCurrentDocCharCount(UniMode u)
 {
-	if (u != uniUTF8 && u != uniCookie)
+	if (u != uniUTF8 && u != uniUTF8_NoBOM)
 	{
 		size_t numLines = _pEditView->execute(SCI_GETLINECOUNT);
 		auto result = _pEditView->execute(SCI_GETLENGTH);
@@ -4299,7 +4310,7 @@ size_t Notepad_plus::getCurrentDocCharCount(UniMode u)
 
 bool Notepad_plus::isFormatUnicode(UniMode u)
 {
-	return (u != uni8Bit && u != uni7Bit && u != uniUTF8 && u != uniCookie);
+	return (u != uni8Bit && u != uni7Bit && u != uniUTF8 && u != uniUTF8_NoBOM);
 }
 
 int Notepad_plus::getBOMSize(UniMode u)
@@ -5160,11 +5171,11 @@ void Notepad_plus::checkUnicodeMenuItems() const
 	int id = -1;
 	switch (um)
 	{
-		case uniUTF8   : id = IDM_FORMAT_UTF_8; break;
-		case uni16BE   : id = IDM_FORMAT_UTF_16BE; break;
-		case uni16LE   : id = IDM_FORMAT_UTF_16LE; break;
-		case uniCookie : id = IDM_FORMAT_AS_UTF_8; break;
-		case uni8Bit   : id = IDM_FORMAT_ANSI; break;
+		case uniUTF8       : id = IDM_FORMAT_UTF_8; break;
+		case uni16BE       : id = IDM_FORMAT_UTF_16BE; break;
+		case uni16LE       : id = IDM_FORMAT_UTF_16LE; break;
+		case uniUTF8_NoBOM : id = IDM_FORMAT_AS_UTF_8; break;
+		case uni8Bit       : id = IDM_FORMAT_ANSI; break;
 
 		case uni7Bit:
 		case uni16BE_NoBOM:
@@ -5174,24 +5185,21 @@ void Notepad_plus::checkUnicodeMenuItems() const
 			break;
 	}
 
-	if (encoding == -1)
+	HMENU _formatMenuHandle = ::GetSubMenu(_mainMenuHandle, MENUINDEX_FORMAT);
+
+	if (encoding == -1) // encoding is not used, so use uniMode to check menu item
 	{
-		// Uncheck all in the sub encoding menu
-        HMENU _formatMenuHandle = ::GetSubMenu(_mainMenuHandle, MENUINDEX_FORMAT);
+		// Uncheck all in the main & sub encoding menu
         doCheck(_formatMenuHandle, -1);
 
-		if (id == -1) //um == uni16BE_NoBOM || um == uni16LE_NoBOM
+		if (id != -1) 
 		{
-			// Uncheck all in the main encoding menu
-			::CheckMenuRadioItem(_mainMenuHandle, IDM_FORMAT_ANSI, IDM_FORMAT_AS_UTF_8, IDM_FORMAT_ANSI, MF_BYCOMMAND);
-			::CheckMenuItem(_mainMenuHandle, IDM_FORMAT_ANSI, MF_UNCHECKED | MF_BYCOMMAND);
-		}
-		else
-		{
-			::CheckMenuRadioItem(_mainMenuHandle, IDM_FORMAT_ANSI, IDM_FORMAT_AS_UTF_8, id, MF_BYCOMMAND);
+			DWORD state = GetMenuState(_formatMenuHandle, IDM_FORMAT_ANSI, MF_BYCOMMAND);
+			::CheckMenuRadioItem(_mainMenuHandle, (state & MFS_GRAYED) ? IDM_FORMAT_UTF_8 : IDM_FORMAT_ANSI, IDM_FORMAT_AS_UTF_8, id, MF_BYCOMMAND);
 		}
+		// else if (id == -1) => um == uni16BE_NoBOM || um == uni16LE_NoBOM, let all items unchecked.
 	}
-	else
+	else // encoding is used
 	{
 		const EncodingMapper& em = EncodingMapper::getInstance();
 		int cmdID = em.getIndexFromEncoding(encoding);
@@ -5202,12 +5210,7 @@ void Notepad_plus::checkUnicodeMenuItems() const
 		}
 		cmdID += IDM_FORMAT_ENCODE;
 
-		// Uncheck all in the main encoding menu
-		::CheckMenuRadioItem(_mainMenuHandle, IDM_FORMAT_ANSI, IDM_FORMAT_AS_UTF_8, IDM_FORMAT_ANSI, MF_BYCOMMAND);
-		::CheckMenuItem(_mainMenuHandle, IDM_FORMAT_ANSI, MF_UNCHECKED | MF_BYCOMMAND);
-
-		// Check the encoding item
-        HMENU _formatMenuHandle = ::GetSubMenu(_mainMenuHandle, MENUINDEX_FORMAT);
+		// Check the encoding item        
         doCheck(_formatMenuHandle, cmdID);
 	}
 }
diff --git a/PowerEditor/src/NppCommands.cpp b/PowerEditor/src/NppCommands.cpp
index 6e7cd243b..ef7e19b1a 100644
--- a/PowerEditor/src/NppCommands.cpp
+++ b/PowerEditor/src/NppCommands.cpp
@@ -2757,15 +2757,25 @@ void Notepad_plus::command(int id)
 		case IDM_FORMAT_UTF_16LE :
 		case IDM_FORMAT_AS_UTF_8 :
 		{
+			bool isUTF8System = NppParameters::getInstance().isCurrentSystemCodepageUTF8();
+
+			if (isUTF8System && id == IDM_FORMAT_ANSI)
+			{
+				return;
+			}
+
 			Buffer * buf = _pEditView->getCurrentBuffer();
 
+			UniMode originalUm = buf->getUnicodeMode();
+			int originalEncoding = buf->getEncoding();
+
 			UniMode um;
 			bool shouldBeDirty = true;
 			switch (id)
 			{
 				case IDM_FORMAT_AS_UTF_8:
-					shouldBeDirty = buf->getUnicodeMode() != uni8Bit;
-					um = uniCookie;
+					shouldBeDirty = originalUm != uni8Bit;
+					um = uniUTF8_NoBOM;
 					break;
 
 				case IDM_FORMAT_UTF_8:
@@ -2781,11 +2791,11 @@ void Notepad_plus::command(int id)
 					break;
 
 				default : // IDM_FORMAT_ANSI
-					shouldBeDirty = buf->getUnicodeMode() != uniCookie;
+					shouldBeDirty = originalUm != uniUTF8_NoBOM;
 					um = uni8Bit;
 			}
 
-			if (buf->getEncoding() != -1)
+			if (originalEncoding != -1)
 			{
 				if (buf->isDirty())
 				{
@@ -2801,7 +2811,9 @@ void Notepad_plus::command(int id)
 						_pEditView->execute(SCI_EMPTYUNDOBUFFER);
 					}
 					else
+					{
 						return;
+					}
 				}
 
 				if (_pEditView->execute(SCI_CANUNDO) == TRUE)
@@ -2816,26 +2828,35 @@ void Notepad_plus::command(int id)
 						// Do nothing
 					}
 					else
+					{
 						return;
+					}
 				}
 
 				buf->setEncoding(-1);
 
 				if (um == uni8Bit)
-					_pEditView->execute(SCI_SETCODEPAGE, CP_ACP);
+				{
+					NppParameters& nppParams = NppParameters::getInstance();
+					_pEditView->execute(SCI_SETCODEPAGE, !nppParams.isCurrentSystemCodepageUTF8() ? CP_ACP : SC_CP_UTF8);
+				}
 				else
 					buf->setUnicodeMode(um);
+
+				MainFileManager.disableAutoDetectEncoding4Loading();
 				fileReload();
+				MainFileManager.enableAutoDetectEncoding4Loading();
 			}
 			else
 			{
-				if (buf->getUnicodeMode() != um)
+				if (originalUm != um)
 				{
 					buf->setUnicodeMode(um);
 					if (shouldBeDirty)
 						buf->setDirty(true);
 				}
 			}
+
 			break;
 		}
 
@@ -2929,8 +2950,11 @@ void Notepad_plus::command(int id)
             if (!buf->isDirty())
             {
 				buf->setEncoding(encoding);
-				buf->setUnicodeMode(uniCookie);
+				buf->setUnicodeMode(uniUTF8_NoBOM);
+
+				MainFileManager.disableAutoDetectEncoding4Loading();
 				fileReload();
+				MainFileManager.enableAutoDetectEncoding4Loading();
             }
 			break;
 		}
@@ -2971,13 +2995,13 @@ void Notepad_plus::command(int id)
                     if (encoding != -1)
                     {
                         buf->setDirty(true);
-                        buf->setUnicodeMode(uniCookie);
+                        buf->setUnicodeMode(uniUTF8_NoBOM);
                         buf->setEncoding(-1);
                         return;
                     }
 
 					idEncoding = IDM_FORMAT_AS_UTF_8;
-					if (um == uniCookie)
+					if (um == uniUTF8_NoBOM)
 						return;
 
 					if (um != uni8Bit)
diff --git a/PowerEditor/src/Parameters.cpp b/PowerEditor/src/Parameters.cpp
index b09215ffb..291c26570 100644
--- a/PowerEditor/src/Parameters.cpp
+++ b/PowerEditor/src/Parameters.cpp
@@ -1003,9 +1003,12 @@ winVer NppParameters::getWindowsVersion()
 
 NppParameters::NppParameters()
 {
-	//Get windows version
+	// Get windows version
 	_winVersion = getWindowsVersion();
 
+	// Get current system code page
+	_currentSystemCodepage = GetACP();
+
 	// Prepare for default path
 	wchar_t nppPath[MAX_PATH];
 	::GetModuleFileName(NULL, nppPath, MAX_PATH);
@@ -5550,7 +5553,15 @@ void NppParameters::feedGUIParameters(TiXmlNode *node)
 			}
 
 			if (element->Attribute(L"encoding", &i))
-				_nppGUI._newDocDefaultSettings._unicodeMode = (UniMode)i;
+			{
+				if (isCurrentSystemCodepageUTF8() // "Beta: Use Unicode UTF-8 for worldwide language support" option is checked in Windows
+					&& static_cast<UniMode>(i) == uni8Bit) // Notepad++ default new document setting is ANSI
+				{
+					// Force Notepad++ default new document setting from ANSI to UTF-8
+					i = static_cast<int>(uniUTF8);
+				}
+				_nppGUI._newDocDefaultSettings._unicodeMode = static_cast<UniMode>(i);
+			}
 
 			if (element->Attribute(L"lang", &i))
 				_nppGUI._newDocDefaultSettings._lang = (LangType)i;
@@ -5560,7 +5571,7 @@ void NppParameters::feedGUIParameters(TiXmlNode *node)
 
 			const wchar_t* val = element->Attribute(L"openAnsiAsUTF8");
 			if (val)
-				_nppGUI._newDocDefaultSettings._openAnsiAsUtf8 = (lstrcmp(val, L"yes") == 0);
+				_nppGUI._newDocDefaultSettings._openAnsiAsUtf8 = isCurrentSystemCodepageUTF8() ? false : (lstrcmp(val, L"yes") == 0);
 
 			val = element->Attribute(L"addNewDocumentOnStartup");
 			if (val)
diff --git a/PowerEditor/src/Parameters.h b/PowerEditor/src/Parameters.h
index 53205dea3..14d74870f 100644
--- a/PowerEditor/src/Parameters.h
+++ b/PowerEditor/src/Parameters.h
@@ -100,18 +100,17 @@ enum class EolType: std::uint8_t
 EolType convertIntToFormatType(int value, EolType defvalue = EolType::osdefault);
 
 
-
-
 enum UniMode {
 	uni8Bit       = 0,  // ANSI
 	uniUTF8       = 1,  // UTF-8 with BOM
 	uni16BE       = 2,  // UTF-16 Big Endian with BOM
 	uni16LE       = 3,  // UTF-16 Little Endian with BOM
-	uniCookie     = 4,  // UTF-8 without BOM
-	uni7Bit       = 5,  // 
+	uniUTF8_NoBOM = 4,  // UTF-8 without BOM
+	uni7Bit       = 5,  // 0 - 127 ASCII
 	uni16BE_NoBOM = 6,  // UTF-16 Big Endian without BOM
 	uni16LE_NoBOM = 7,  // UTF-16 Little Endian without BOM
-	uniEnd};
+	uniEnd
+};
 
 enum ChangeDetect { cdDisabled = 0x0, cdEnabledOld = 0x01, cdEnabledNew = 0x02, cdAutoUpdate = 0x04, cdGo2end = 0x08 };
 enum BackupFeature {bak_none = 0, bak_simple = 1, bak_verbose = 2};
@@ -612,7 +611,7 @@ private :
 struct NewDocDefaultSettings final
 {
 	EolType _format = EolType::osdefault;
-	UniMode _unicodeMode = uniCookie;
+	UniMode _unicodeMode = uniUTF8_NoBOM;
 	bool _openAnsiAsUtf8 = true;
 	LangType _lang = L_TEXT;
 	int _codepage = -1; // -1 when not using
@@ -1821,6 +1820,20 @@ public:
 	winVer getWinVersion() const {return _winVersion;};
 	std::wstring getWinVersionStr() const;
 	std::wstring getWinVerBitStr() const;
+
+	int currentSystemCodepage() const { return _currentSystemCodepage; };
+	bool isCurrentSystemCodepageUTF8() const { return _currentSystemCodepage == 65001; };
+	int defaultCodepage() const { // return all the codepage except UTF8 (65001)
+		if (isCurrentSystemCodepageUTF8())
+		{
+			int localCodepage = 0;
+			// Get the system default codepage, which is the codepage before "Beta: Use Unicode UTF-8 for worldwide language support" option being checked
+			GetLocaleInfoEx(LOCALE_NAME_SYSTEM_DEFAULT, LOCALE_IDEFAULTANSICODEPAGE | LOCALE_RETURN_NUMBER, reinterpret_cast<LPTSTR>(&localCodepage), 2);
+			return localCodepage;
+		}
+		return _currentSystemCodepage;
+	};
+
 	FindHistory & getFindHistory() {return _findHistory;};
 	bool _isFindReplacing = false; // an on the fly variable for find/replace functions
 #ifndef	_WIN64
@@ -2085,6 +2098,8 @@ private:
 	bool _isPlaceHolderEnabled = false;
 	bool _theWarningHasBeenGiven = false;
 
+	int _currentSystemCodepage = -1;
+
 public:
 	std::wstring getWingupFullPath() const { return _wingupFullPath; };
 	std::wstring getWingupParams() const { return _wingupParams; };
diff --git a/PowerEditor/src/ScintillaComponent/Buffer.cpp b/PowerEditor/src/ScintillaComponent/Buffer.cpp
index 2d88e2454..09f56a382 100644
--- a/PowerEditor/src/ScintillaComponent/Buffer.cpp
+++ b/PowerEditor/src/ScintillaComponent/Buffer.cpp
@@ -89,7 +89,7 @@ Buffer::Buffer(FileManager * pManager, BufferID id, Document doc, DocFileStatus
 	_unicodeMode = ndds._unicodeMode;
 	_encoding = ndds._codepage;
 	if (_encoding != -1)
-		_unicodeMode = uniCookie;
+		_unicodeMode = uniUTF8_NoBOM;
 
 	_currentStatus = type;
 
@@ -1005,7 +1005,7 @@ bool FileManager::reloadBuffer(BufferID id)
 {
 	Buffer* buf = getBufferByID(id);
 	Document doc = buf->getDocument();
-	Utf8_16_Read UnicodeConvertor;
+	Utf8_16_Read unicodeConvertor;
 
 	LoadedFileFormat loadedFileFormat;
 	loadedFileFormat._encoding = buf->getEncoding();
@@ -1037,7 +1037,7 @@ bool FileManager::reloadBuffer(BufferID id)
 	char* data = new char[blockSize + 8]; // +8 for incomplete multibyte char
 
 	buf->_canNotify = false;	//disable notify during file load, we don't want dirty status to be triggered
-	bool res = loadFileData(doc, fileSize, buf->getFullPathName(), data, &UnicodeConvertor, loadedFileFormat);
+	bool res = loadFileData(doc, fileSize, buf->getFullPathName(), data, &unicodeConvertor, loadedFileFormat);
 	buf->_canNotify = true;
 
 	delete[] data;
@@ -1050,7 +1050,7 @@ bool FileManager::reloadBuffer(BufferID id)
 
 		buf->setSavePointDirty(false);
 
-		setLoadedBufferEncodingAndEol(buf, UnicodeConvertor, loadedFileFormat._encoding, loadedFileFormat._eolFormat);
+		setLoadedBufferEncodingAndEol(buf, unicodeConvertor, loadedFileFormat._encoding, loadedFileFormat._eolFormat);
 	}
 
 	return res;
@@ -1059,24 +1059,28 @@ bool FileManager::reloadBuffer(BufferID id)
 
 void FileManager::setLoadedBufferEncodingAndEol(Buffer* buf, const Utf8_16_Read& UnicodeConvertor, int encoding, EolType bkformat)
 {
-	if (encoding == -1)
+	int encoding2Set = encoding;
+	UniMode unimode2Set = UnicodeConvertor.getEncoding();
+
+	if (encoding2Set == -1)
 	{
 		NppParameters& nppParamInst = NppParameters::getInstance();
 		const NewDocDefaultSettings & ndds = (nppParamInst.getNppGUI()).getNewDocDefaultSettings();
-
-		UniMode um = UnicodeConvertor.getEncoding();
-		if (um == uni7Bit)
-			um = (ndds._openAnsiAsUtf8) ? uniCookie : uni8Bit;
-
-		buf->setUnicodeMode(um);
+		
+		if (unimode2Set == uni7Bit)
+			unimode2Set = (ndds._openAnsiAsUtf8) ? uniUTF8_NoBOM : uni8Bit;
 	}
 	else
 	{
 		// Test if encoding is set to UTF8 w/o BOM (usually for utf8 indicator of xml or html)
-		buf->setEncoding((encoding == SC_CP_UTF8)?-1:encoding);
-		buf->setUnicodeMode(uniCookie);
+		encoding2Set = ((encoding2Set == SC_CP_UTF8) ? -1 : encoding2Set);
+		unimode2Set = uniUTF8_NoBOM;
 	}
 
+	buf->setEncoding(encoding2Set);
+	buf->setUnicodeMode(unimode2Set);
+
+
 	// Since the buffer will be reloaded from the disk, EOL might have been changed
 	if (bkformat != EolType::unknown)
 		buf->setEolFormat(bkformat);
@@ -1208,7 +1212,7 @@ bool FileManager::backupCurrentBuffer()
 		if (buffer->isModified()) // buffer dirty and modified, write the backup file
 		{
 			UniMode mode = buffer->getUnicodeMode();
-			if (mode == uniCookie)
+			if (mode == uniUTF8_NoBOM)
 				mode = uni8Bit;	//set the mode to ANSI to prevent converter from adding BOM and performing conversions, Scintilla's data can be copied directly
 
 			Utf8_16_Write UnicodeConvertor;
@@ -1421,7 +1425,7 @@ SavingStatus FileManager::saveBuffer(BufferID id, const wchar_t* filename, bool
 	}
 
 	UniMode mode = buffer->getUnicodeMode();
-	if (mode == uniCookie)
+	if (mode == uniUTF8_NoBOM)
 		mode = uni8Bit;	//set the mode to ANSI to prevent converter from adding BOM and performing conversions, Scintilla's data can be copied directly
 
 	Utf8_16_Write UnicodeConvertor;
@@ -1942,23 +1946,34 @@ bool FileManager::loadFileData(Document doc, int64_t fileSize, const wchar_t * f
 
 			if (lenFile == 0) break;
 
+			bool hasBOM = false;
             if (isFirstTime)
             {
-				const NppGUI& nppGui = NppParameters::getInstance().getNppGUI();
+				NppParameters& nppParamInst = NppParameters::getInstance();
+				const NppGUI& nppGui = nppParamInst.getNppGUI();
+
+				//
+				// Detect encoding
+				//
 
 				// check if file contain any BOM
-                if (Utf8_16_Read::determineEncoding((unsigned char *)data, lenFile) != uni8Bit)
-                {
-                    // if file contains any BOM, then encoding will be erased,
-                    // and the document will be interpreted as UTF
+				if (Utf8_16_Read::determineEncodingFromBOM((unsigned char*)data, lenFile) != uni8Bit)
+				{
+					// if file contains any BOM, then encoding will be erased,
+					// and the document will be interpreted as UTF
 					fileFormat._encoding = -1;
+					hasBOM = true;
 				}
 				else if (fileFormat._encoding == -1)
 				{
-					if (nppGui._detectEncoding)
+					if (nppGui._detectEncoding && !isAutoDetectEncodingDisabled4Loading)
 						fileFormat._encoding = detectCodepage(data, lenFile);
-                }
-				
+				}
+
+				//
+				// Detect programming language
+				//
+
 				bool isLargeFile = fileSize >= nppGui._largeFileRestriction._largeFileSizeDefInByte;
 				if (!isLargeFile && fileFormat._language == L_TEXT)
 				{
@@ -1969,6 +1984,7 @@ bool FileManager::loadFileData(Document doc, int64_t fileSize, const wchar_t * f
                 isFirstTime = false;
             }
 
+
 			if (fileFormat._encoding != -1)
 			{
 				if (fileFormat._encoding == SC_CP_UTF8)
@@ -1980,19 +1996,52 @@ bool FileManager::loadFileData(Document doc, int64_t fileSize, const wchar_t * f
 				{
 					WcharMbcsConvertor& wmc = WcharMbcsConvertor::getInstance();
 					int newDataLen = 0;
-					const char *newData = wmc.encode(fileFormat._encoding, SC_CP_UTF8, data, static_cast<int32_t>(lenFile), &newDataLen, &incompleteMultibyteChar);
+					const char* newData = wmc.encode(fileFormat._encoding, SC_CP_UTF8, data, static_cast<int32_t>(lenFile), &newDataLen, &incompleteMultibyteChar);
 					_pscratchTilla->execute(SCI_APPENDTEXT, newDataLen, reinterpret_cast<LPARAM>(newData));
 				}
 
 				if (format == EolType::unknown)
 					format = getEOLFormatForm(data, lenFile, EolType::unknown);
 			}
-			else
+			else // (fileFormat._encoding == -1) => encoding not found yet or BOM found
 			{
+				NppParameters& nppParamInst = NppParameters::getInstance();
 				lenConvert = unicodeConvertor->convert(data, lenFile);
-				_pscratchTilla->execute(SCI_APPENDTEXT, lenConvert, reinterpret_cast<LPARAM>(unicodeConvertor->getNewBuf()));
-				if (format == EolType::unknown)
-					format = getEOLFormatForm(unicodeConvertor->getNewBuf(), unicodeConvertor->getNewSize(), EolType::unknown);
+
+				if (!nppParamInst.isCurrentSystemCodepageUTF8()) // Default mode: all other encodings
+				{
+					_pscratchTilla->execute(SCI_APPENDTEXT, lenConvert, reinterpret_cast<LPARAM>(unicodeConvertor->getNewBuf()));
+					if (format == EolType::unknown)
+						format = getEOLFormatForm(unicodeConvertor->getNewBuf(), unicodeConvertor->getNewSize(), EolType::unknown);
+				}
+				else // "Use Unicode UTF-8 for worldwide language support" option is enabled 
+				{
+					UniMode uniMode = unicodeConvertor->getEncoding();
+
+					if (hasBOM || // uniUTF8, uni16BE, uni16LE
+						uniMode == uni16BE_NoBOM || uniMode == uni16LE_NoBOM || uniMode == uniUTF8_NoBOM || uniMode == uni7Bit)
+					{
+						if (uniMode == uni7Bit)
+							fileFormat._encoding = nppParamInst.currentSystemCodepage();
+
+						_pscratchTilla->execute(SCI_APPENDTEXT, lenConvert, reinterpret_cast<LPARAM>(unicodeConvertor->getNewBuf()));
+
+						if (format == EolType::unknown)
+							format = getEOLFormatForm(unicodeConvertor->getNewBuf(), unicodeConvertor->getNewSize(), EolType::unknown);
+					}
+					else // if (uniMode == uni8Bit)
+					{
+						WcharMbcsConvertor& wmc = WcharMbcsConvertor::getInstance();
+						int newDataLen = 0;
+						fileFormat._encoding = nppParamInst.defaultCodepage();
+
+						const char* newData = wmc.encode(fileFormat._encoding, SC_CP_UTF8, data, static_cast<int32_t>(lenFile), &newDataLen, &incompleteMultibyteChar);
+						_pscratchTilla->execute(SCI_APPENDTEXT, newDataLen, reinterpret_cast<LPARAM>(newData));
+
+						if (format == EolType::unknown)
+							format = getEOLFormatForm(data, lenFile, EolType::unknown);
+					}
+				}
 			}
 
 			sciStatus = static_cast<int>(_pscratchTilla->execute(SCI_GETSTATUS));
@@ -2060,7 +2109,7 @@ bool FileManager::loadFileData(Document doc, int64_t fileSize, const wchar_t * f
 		//for empty files, if the default for new files is UTF8, and "Apply to opened ANSI files" is set, apply it
 		if ((fileSize == 0) && (fileFormat._encoding < 1))
 		{
-			if (ndds._unicodeMode == uniCookie && ndds._openAnsiAsUtf8)
+			if (ndds._unicodeMode == uniUTF8_NoBOM && ndds._openAnsiAsUtf8)
 				fileFormat._encoding = SC_CP_UTF8;
 		}
 	}
diff --git a/PowerEditor/src/ScintillaComponent/Buffer.h b/PowerEditor/src/ScintillaComponent/Buffer.h
index 1a838f817..8fe35c54b 100644
--- a/PowerEditor/src/ScintillaComponent/Buffer.h
+++ b/PowerEditor/src/ScintillaComponent/Buffer.h
@@ -117,11 +117,16 @@ public:
 	void removeHotSpot(Buffer * buffer) const;
 	size_t nextUntitledNewNumber() const;
 
+	void enableAutoDetectEncoding4Loading() { isAutoDetectEncodingDisabled4Loading = false; };
+	void disableAutoDetectEncoding4Loading() { isAutoDetectEncodingDisabled4Loading = true; }; // Disable the encoding auto-detection on loading file while switching among the different encoding.
+	                                                                                           // The value of isAutoDetectEncodingDisabled4Loading will be restored to false after each file loading 
+	                                                                                           // to restore the encoding auto-detection ability for other file loading operations. 
+
 private:
 	struct LoadedFileFormat {
 		LoadedFileFormat() = default;
 		LangType _language = L_TEXT;
-		int _encoding = 0;
+		int _encoding = uni8Bit;
 		EolType _eolFormat = EolType::osdefault;
 	};
 
@@ -137,6 +142,8 @@ private:
 	FileManager& operator=(FileManager&&) = delete;
 
 	int detectCodepage(char* buf, size_t len);
+	bool isAutoDetectEncodingDisabled4Loading = false;
+
 	bool loadFileData(Document doc, int64_t fileSize, const wchar_t* filename, char* buffer, Utf8_16_Read* UnicodeConvertor, LoadedFileFormat& fileFormat);
 	LangType detectLanguageFromTextBeginning(const unsigned char *data, size_t dataLen);
 
@@ -409,8 +416,12 @@ private:
 	std::wstring _userLangExt; // it's useful if only (_lang == L_USER)
 	bool _isDirty = false;
 	EolType _eolFormat = EolType::osdefault;
-	UniMode _unicodeMode = uniUTF8;
+
+	// if _encoding == -1, then _unicodeMode is used.
+	// otherwise _encoding is used.
 	int _encoding = -1;
+	UniMode _unicodeMode = uniUTF8;
+
 	bool _isUserReadOnly = false;
 	bool _isFromNetwork = false;
 	bool _needLexer = false; // new buffers do not need lexing, Scintilla takes care of that
diff --git a/PowerEditor/src/ScintillaComponent/ScintillaEditView.cpp b/PowerEditor/src/ScintillaComponent/ScintillaEditView.cpp
index 8d3e84778..113a12936 100644
--- a/PowerEditor/src/ScintillaComponent/ScintillaEditView.cpp
+++ b/PowerEditor/src/ScintillaComponent/ScintillaEditView.cpp
@@ -343,7 +343,7 @@ void ScintillaEditView::init(HINSTANCE hInst, HWND hPere)
 		// so that existing plugins using SCI_SETTECHNOLOGY behave like before
 	}
 
-	_codepage = ::GetACP();
+	_codepage = nppParams.currentSystemCodepage();
 
 	::SetWindowLongPtr(_hSelf, GWLP_USERDATA, reinterpret_cast<LONG_PTR>(this));
 	_callWindowProc = CallWindowProc;
@@ -1012,7 +1012,7 @@ void ScintillaEditView::setUserLexer(const wchar_t *userLangName)
 	int encoding = _currentBuffer->getEncoding();
 	if (encoding == -1)
 	{
-		if (unicodeMode == uniUTF8 || unicodeMode == uniCookie)
+		if (unicodeMode == uniUTF8 || unicodeMode == uniUTF8_NoBOM)
 			codepage = CP_UTF8;
 	}
 	else
@@ -2461,10 +2461,12 @@ void ScintillaEditView::bufferUpdated(Buffer * buffer, int mask)
 		{
 			execute(SCI_SETEOLMODE, static_cast<int>(_currentBuffer->getEolFormat()));
 		}
+
 		if (mask & BufferChangeReadonly)
 		{
 			execute(SCI_SETREADONLY, _currentBuffer->isReadOnly());
 		}
+
 		if (mask & BufferChangeUnicode)
 		{
             int enc = CP_ACP;
diff --git a/PowerEditor/src/ScintillaComponent/ScintillaEditView.h b/PowerEditor/src/ScintillaComponent/ScintillaEditView.h
index dedf486ea..c8a351185 100644
--- a/PowerEditor/src/ScintillaComponent/ScintillaEditView.h
+++ b/PowerEditor/src/ScintillaComponent/ScintillaEditView.h
@@ -874,6 +874,7 @@ protected:
 	Buffer* _currentBuffer = nullptr;
 
 	int _codepage = CP_ACP;
+
 	bool _wrapRestoreNeeded = false;
 	bool _positionRestoreNeeded = false;
 	uint32_t _restorePositionRetryCount = 0;
diff --git a/PowerEditor/src/Utf8_16.cpp b/PowerEditor/src/Utf8_16.cpp
index 861e42089..eaf1a10d1 100644
--- a/PowerEditor/src/Utf8_16.cpp
+++ b/PowerEditor/src/Utf8_16.cpp
@@ -140,7 +140,7 @@ size_t Utf8_16_Read::convert(char* buf, size_t len)
     {
 		case uni7Bit:
         case uni8Bit:
-        case uniCookie:
+        case uniUTF8_NoBOM:
 		{
             // Do nothing, pass through
 			m_nAllocatedBufSize = 0;
@@ -249,8 +249,9 @@ void Utf8_16_Read::determineEncoding()
 	else
 	{
 		u78 detectedEncoding = utf8_7bits_8bits();
+
 		if (detectedEncoding == utf8NoBOM)
-			m_eEncoding = uniCookie;
+			m_eEncoding = uniUTF8_NoBOM;
 		else if (detectedEncoding == ascii7bits)
 			m_eEncoding = uni7Bit;
 		else //(detectedEncoding == ascii8bits)
@@ -259,7 +260,7 @@ void Utf8_16_Read::determineEncoding()
 	}
 }
 
-UniMode Utf8_16_Read::determineEncoding(const unsigned char *buf, size_t bufLen)
+UniMode Utf8_16_Read::determineEncodingFromBOM(const unsigned char *buf, size_t bufLen)
 {
     // detect UTF-16 big-endian with BOM
 	if (bufLen > 1 && buf[0] == k_Boms[uni16BE][0] && buf[1] == k_Boms[uni16BE][1])
@@ -369,7 +370,7 @@ bool Utf8_16_Write::writeFile(const void* p, size_t _size)
 	{
 		case uni7Bit:
 		case uni8Bit:
-		case uniCookie:
+		case uniUTF8_NoBOM:
 		case uniUTF8:
 		{
 			// Normal write
@@ -436,7 +437,7 @@ size_t Utf8_16_Write::convert(char* p, size_t _size)
 		{
 		case uni7Bit:
 		case uni8Bit:
-		case uniCookie:
+		case uniUTF8_NoBOM:
 		{
 			// Normal write
 			m_pNewBuf = new ubyte[_size];
diff --git a/PowerEditor/src/Utf8_16.h b/PowerEditor/src/Utf8_16.h
index 75766dc72..5eafe5b5c 100644
--- a/PowerEditor/src/Utf8_16.h
+++ b/PowerEditor/src/Utf8_16.h
@@ -113,14 +113,14 @@ public:
 	size_t getNewSize() const { return m_nNewBufSize; }
 
 	UniMode getEncoding() const { return m_eEncoding; }
-    static UniMode determineEncoding(const unsigned char *buf, size_t bufLen);
+    static UniMode determineEncodingFromBOM(const unsigned char *buf, size_t bufLen);
 
 protected:
 	void determineEncoding();
 
 	u78 utf8_7bits_8bits();
 private:
-	UniMode    m_eEncoding = uni8Bit;
+	UniMode         m_eEncoding = uni8Bit;
 	ubyte*          m_pBuf = nullptr;
 	ubyte*          m_pNewBuf = nullptr;
 	// size of the new buffer
diff --git a/PowerEditor/src/WinControls/AboutDlg/AboutDlg.cpp b/PowerEditor/src/WinControls/AboutDlg/AboutDlg.cpp
index dc23882f4..d3311e23e 100644
--- a/PowerEditor/src/WinControls/AboutDlg/AboutDlg.cpp
+++ b/PowerEditor/src/WinControls/AboutDlg/AboutDlg.cpp
@@ -516,7 +516,7 @@ intptr_t CALLBACK DebugInfoDlg::run_dlgProc(UINT message, WPARAM wParam, LPARAM
 			{
 				constexpr size_t bufSizeACP = 32;
 				wchar_t szACP[bufSizeACP] = { '\0' };
-				swprintf(szACP, bufSizeACP, L"%u", ::GetACP());
+				swprintf(szACP, bufSizeACP, L"%u", nppParam.currentSystemCodepage());
 				_debugInfoStr += L"Current ANSI codepage: ";
  				_debugInfoStr += szACP;
 				_debugInfoStr += L"\r\n";
diff --git a/PowerEditor/src/WinControls/Preference/preference.rc b/PowerEditor/src/WinControls/Preference/preference.rc
index 31ae5e6da..c13efd9db 100644
--- a/PowerEditor/src/WinControls/Preference/preference.rc
+++ b/PowerEditor/src/WinControls/Preference/preference.rc
@@ -255,7 +255,7 @@ BEGIN
     CONTROL         "Macintosh (CR)",IDC_RADIO_F_MAC,"Button",BS_AUTORADIOBUTTON,65,80,70,10
     GROUPBOX        "Encoding",IDC_ENCODING_STATIC,232,28,175,122,BS_CENTER
     CONTROL         "ANSI",IDC_RADIO_ANSI,"Button",BS_AUTORADIOBUTTON | WS_GROUP,242,39,150,10
-    CONTROL         "UTF-8",IDC_RADIO_UTF8SANSBOM,"Button",BS_AUTORADIOBUTTON,242,53,150,10
+    CONTROL         "UTF-8",IDC_RADIO_UTF8_NO_BOM,"Button",BS_AUTORADIOBUTTON,242,53,150,10
     CONTROL         "Apply to opened ANSI files",IDC_CHECK_OPENANSIASUTF8, "Button",BS_AUTOCHECKBOX | WS_TABSTOP,252,65,150,10
     CONTROL         "UTF-8 with BOM",IDC_RADIO_UTF8,"Button",BS_AUTORADIOBUTTON,242,79,150,10
     CONTROL         "UTF-16 Big Endian with BOM",IDC_RADIO_UTF16BIG,"Button",BS_AUTORADIOBUTTON,242,95,150,10
diff --git a/PowerEditor/src/WinControls/Preference/preferenceDlg.cpp b/PowerEditor/src/WinControls/Preference/preferenceDlg.cpp
index 12990a707..a431f4c91 100644
--- a/PowerEditor/src/WinControls/Preference/preferenceDlg.cpp
+++ b/PowerEditor/src/WinControls/Preference/preferenceDlg.cpp
@@ -3360,6 +3360,14 @@ intptr_t CALLBACK MiscSubDlg::run_dlgProc(UINT message, WPARAM wParam, LPARAM)
 	return FALSE;
 }
 
+
+void NewDocumentSubDlg::makeOpenAnsiAsUtf8(bool doIt) const
+{
+	if (!doIt)
+		::SendDlgItemMessage(_hSelf, IDC_CHECK_OPENANSIASUTF8, BM_SETCHECK, BST_UNCHECKED, 0);
+	::EnableWindow(::GetDlgItem(_hSelf, IDC_CHECK_OPENANSIASUTF8), doIt && !NppParameters::getInstance().isCurrentSystemCodepageUTF8());
+}
+
 intptr_t CALLBACK NewDocumentSubDlg::run_dlgProc(UINT message, WPARAM wParam, LPARAM)
 {
 	NppParameters& nppParam = NppParameters::getInstance();
@@ -3399,8 +3407,8 @@ intptr_t CALLBACK NewDocumentSubDlg::run_dlgProc(UINT message, WPARAM wParam, LP
 				case uniUTF8 :
 					ID2Check = IDC_RADIO_UTF8;
 					break;
-				case uniCookie :
-					ID2Check = IDC_RADIO_UTF8SANSBOM;
+				case uniUTF8_NoBOM :
+					ID2Check = IDC_RADIO_UTF8_NO_BOM;
 					break;
 
 				default : //uni8Bit
@@ -3435,8 +3443,15 @@ intptr_t CALLBACK NewDocumentSubDlg::run_dlgProc(UINT message, WPARAM wParam, LP
 			}
 
 			::SendDlgItemMessage(_hSelf, ID2Check, BM_SETCHECK, BST_CHECKED, 0);
-			::SendDlgItemMessage(_hSelf, IDC_CHECK_OPENANSIASUTF8, BM_SETCHECK, (ID2Check == IDC_RADIO_UTF8SANSBOM && ndds._openAnsiAsUtf8)?BST_CHECKED:BST_UNCHECKED, 0);
-			::EnableWindow(::GetDlgItem(_hSelf, IDC_CHECK_OPENANSIASUTF8), ID2Check == IDC_RADIO_UTF8SANSBOM);
+			::SendDlgItemMessage(_hSelf, IDC_CHECK_OPENANSIASUTF8, BM_SETCHECK, (ID2Check == IDC_RADIO_UTF8_NO_BOM && ndds._openAnsiAsUtf8)?BST_CHECKED:BST_UNCHECKED, 0);
+
+			bool isEnableAnsiAsUTF = ID2Check == IDC_RADIO_UTF8_NO_BOM;
+			if (nppParam.isCurrentSystemCodepageUTF8())
+			{
+				isEnableAnsiAsUTF = false;
+				::EnableWindow(::GetDlgItem(_hSelf, IDC_RADIO_ANSI), false);
+			}
+			::EnableWindow(::GetDlgItem(_hSelf, IDC_CHECK_OPENANSIASUTF8), isEnableAnsiAsUTF);
 
 			for (int i = L_TEXT + 1 ; i < nppParam.L_END ; ++i) // Skip L_TEXT
 			{
@@ -3525,8 +3540,8 @@ intptr_t CALLBACK NewDocumentSubDlg::run_dlgProc(UINT message, WPARAM wParam, LP
 					ndds._codepage = -1;
 					::EnableWindow(::GetDlgItem(_hSelf, IDC_COMBO_OTHERCP), false);
 					return TRUE;
-				case IDC_RADIO_UTF8SANSBOM:
-					ndds._unicodeMode = uniCookie;
+				case IDC_RADIO_UTF8_NO_BOM:
+					ndds._unicodeMode = uniUTF8_NoBOM;
 					makeOpenAnsiAsUtf8(true);
 					ndds._codepage = -1;
 					::EnableWindow(::GetDlgItem(_hSelf, IDC_COMBO_OTHERCP), false);
diff --git a/PowerEditor/src/WinControls/Preference/preferenceDlg.h b/PowerEditor/src/WinControls/Preference/preferenceDlg.h
index 1624e9716..5f0506a9b 100644
--- a/PowerEditor/src/WinControls/Preference/preferenceDlg.h
+++ b/PowerEditor/src/WinControls/Preference/preferenceDlg.h
@@ -186,11 +186,7 @@ public :
 	NewDocumentSubDlg() = default;
 
 private :
-	void makeOpenAnsiAsUtf8(bool doIt){
-		if (!doIt)
-			::SendDlgItemMessage(_hSelf, IDC_CHECK_OPENANSIASUTF8, BM_SETCHECK, BST_UNCHECKED, 0);
-		::EnableWindow(::GetDlgItem(_hSelf, IDC_CHECK_OPENANSIASUTF8), doIt);
-	};
+	void makeOpenAnsiAsUtf8(bool doIt) const;
 	intptr_t CALLBACK run_dlgProc(UINT message, WPARAM wParam, LPARAM lParam) override;
 };
 
diff --git a/PowerEditor/src/WinControls/Preference/preference_rc.h b/PowerEditor/src/WinControls/Preference/preference_rc.h
index 608b80447..15b616862 100644
--- a/PowerEditor/src/WinControls/Preference/preference_rc.h
+++ b/PowerEditor/src/WinControls/Preference/preference_rc.h
@@ -295,7 +295,7 @@
 #define IDC_RADIO_F_MAC                                6404
 #define IDC_ENCODING_STATIC                            6405
 #define IDC_RADIO_ANSI                                 6406
-#define IDC_RADIO_UTF8SANSBOM                          6407
+#define IDC_RADIO_UTF8_NO_BOM                          6407
 #define IDC_RADIO_UTF8                                 6408
 #define IDC_RADIO_UTF16BIG                             6409
 #define IDC_RADIO_UTF16SMALL                           6410