diff --git a/test/intl402/Locale/constructor-options-firstDayOfWeek-invalid.js b/test/intl402/Locale/constructor-options-firstDayOfWeek-invalid.js
new file mode 100644
index 0000000000..a2a754d923
--- /dev/null
+++ b/test/intl402/Locale/constructor-options-firstDayOfWeek-invalid.js
@@ -0,0 +1,31 @@
+// Copyright 2023 Google Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-intl.locale
+description: >
+    Checks error cases for the options argument to the Locale constructor.
+info: |
+    Intl.Locale( tag [, options] )
+
+    ...
+    x. Let numberingSystem be ? GetOption(options, "firstDayOfWeek", "string", < *"mon"*, *"tue"*, *"wed"*, *"thu"*, *"fri"*, *"sat"*, *"sun"*, *"0"*, *"1"*, *"2"*, *"3"*, *"4"*, *"5"*, *"6"*, *"7"*> , undefined).
+    ...
+
+features: [Intl.Locale,Intl.Locale-info]
+---*/
+
+const invalidFirstDayOfWeekOptions = [
+  "",
+  "m",
+  "mo",
+  "monday",
+  true,
+  false,
+  null,
+];
+for (const firstDayOfWeek of invalidFirstDayOfWeekOptions) {
+  assert.throws(RangeError, function() {
+    new Intl.Locale('en', {firstDayOfWeek});
+  }, `new Intl.Locale("en", {firstDayOfWeek: "${firstDayOfWeek}"}) throws RangeError`);
+}
diff --git a/test/intl402/Locale/constructor-options-firstDayOfWeek-valid.js b/test/intl402/Locale/constructor-options-firstDayOfWeek-valid.js
new file mode 100644
index 0000000000..d9efe8bf82
--- /dev/null
+++ b/test/intl402/Locale/constructor-options-firstDayOfWeek-valid.js
@@ -0,0 +1,65 @@
+// Copyright 2023 Google Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-intl.locale
+description: >
+    Checks valid cases for the options argument to the Locale constructor.
+info: |
+    Intl.Locale( tag [, options] )
+
+    ...
+    x. Let numberingSystem be ? GetOption(options, "firstDayOfWeek", "string", < *"mon"*, *"tue"*, *"wed"*, *"thu"*, *"fri"*, *"sat"*, *"sun"*, *"0"*, *"1"*, *"2"*, *"3"*, *"4"*, *"5"*, *"6"*, *"7"*> , undefined).
+    x. Let firstDay be *undefined*.
+    x. If fw is not *undefined*, then
+       x. Set firstDay to !WeekdayToString(fw).
+       x. Set opt.[[fw]] to firstDay.
+    ...
+    x. Let r be ! ApplyUnicodeExtensionToTag(tag, opt, relevantExtensionKeys).
+    ...
+    x. Let firstDay be *undefined*.
+    x. If r.[[fw]] is not *undefined*, then
+       x. Set firstDay to ! WeekdayToNumber(r.[[fw]]).
+       x. Set locale.[[FirstDayOfWeek]] to firstDay.
+    ...
+
+features: [Intl.Locale,Intl.Locale-info]
+---*/
+
+const validFirstDayOfWeekOptions = [
+  ["mon", "en-u-fw-mon"],
+  ["tue", "en-u-fw-tue"],
+  ["wed", "en-u-fw-wed"],
+  ["thu", "en-u-fw-thu"],
+  ["fri", "en-u-fw-fri"],
+  ["sat", "en-u-fw-sat"],
+  ["sun", "en-u-fw-sun"],
+  ["1", "en-u-fw-mon"],
+  ["2", "en-u-fw-tue"],
+  ["3", "en-u-fw-wed"],
+  ["4", "en-u-fw-thu"],
+  ["5", "en-u-fw-fri"],
+  ["6", "en-u-fw-sat"],
+  ["7", "en-u-fw-sun"],
+  ["0", "en-u-fw-sun"],
+  [1, "en-u-fw-mon"],
+  [2, "en-u-fw-tue"],
+  [3, "en-u-fw-wed"],
+  [4, "en-u-fw-thu"],
+  [5, "en-u-fw-fri"],
+  [6, "en-u-fw-sat"],
+  [7, "en-u-fw-sun"],
+  [0, "en-u-fw-sun"],
+];
+for (const [firstDayOfWeek, expected] of validFirstDayOfWeekOptions) {
+  assert.sameValue(
+    new Intl.Locale('en', { firstDayOfWeek }).toString(),
+    expected,
+    `new Intl.Locale("en", { firstDayOfWeek: ${firstDayOfWeek} }).toString() returns "${expected}"`
+  );
+  assert.sameValue(
+    new Intl.Locale('en-u-fw-WED', { firstDayOfWeek }).toString(),
+    expected,
+    `new Intl.Locale("en-u-fw-WED", { firstDayOfWeek: ${firstDayOfWeek} }).toString() returns "${expected}"`
+  );
+}
diff --git a/test/intl402/Locale/prototype/firstDayOfWeek/branding.js b/test/intl402/Locale/prototype/firstDayOfWeek/branding.js
new file mode 100644
index 0000000000..cfc161854c
--- /dev/null
+++ b/test/intl402/Locale/prototype/firstDayOfWeek/branding.js
@@ -0,0 +1,30 @@
+// Copyright 2023 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-Intl.Locale.prototype.firstDayOfWeek
+description: >
+    Verifies the branding check for the "firstDayOfWeek" property of the Locale prototype object.
+info: |
+    Intl.Locale.prototype.firstDayOfWeek
+
+    2. If Type(loc) is not Object or loc does not have an [[InitializedLocale]] internal slot, then
+        a. Throw a TypeError exception.
+features: [Intl.Locale,Intl.Locale-info]
+---*/
+
+const propdesc = Object.getOwnPropertyDescriptor(Intl.Locale.prototype, "firstDayOfWeek");
+const invalidValues = [
+  undefined,
+  null,
+  true,
+  "",
+  Symbol(),
+  1,
+  {},
+  Intl.Locale.prototype,
+];
+
+for (const invalidValue of invalidValues) {
+  assert.throws(TypeError, () => propdesc.get.call(invalidValue));
+}
diff --git a/test/intl402/Locale/prototype/firstDayOfWeek/name.js b/test/intl402/Locale/prototype/firstDayOfWeek/name.js
new file mode 100644
index 0000000000..1b1bb3a2e5
--- /dev/null
+++ b/test/intl402/Locale/prototype/firstDayOfWeek/name.js
@@ -0,0 +1,22 @@
+// Copyright 2023 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-intl.locale.prototype.firstDayOfWeek
+description: >
+    Checks the "name" property of Intl.Locale.prototype.firstDayOfWeek.
+info: |
+    Unless specified otherwise in this document, the objects, functions, and constructors described in this standard are subject to the generic requirements and restrictions specified for standard built-in ECMAScript objects in the ECMAScript 2019 Language Specification, 10th edition, clause 17, or successor.
+    Every built-in function object, including constructors, that is not identified as an anonymous function has a name property whose value is a String. Unless otherwise specified, this value is the name that is given to the function in this specification. Functions that are specified as get or set accessor functions of built-in properties have "get " or "set " prepended to the property name string.
+    Unless otherwise specified, the name property of a built-in function object, if it exists, has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
+includes: [propertyHelper.js]
+features: [Intl.Locale,Intl.Locale-info]
+---*/
+
+const getter = Object.getOwnPropertyDescriptor(Intl.Locale.prototype, "firstDayOfWeek").get;
+verifyProperty(getter, "name", {
+  value: "get firstDayOfWeek",
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});
diff --git a/test/intl402/Locale/prototype/firstDayOfWeek/prop-desc.js b/test/intl402/Locale/prototype/firstDayOfWeek/prop-desc.js
new file mode 100644
index 0000000000..3c4d81bdd5
--- /dev/null
+++ b/test/intl402/Locale/prototype/firstDayOfWeek/prop-desc.js
@@ -0,0 +1,25 @@
+// Copyright 2023 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-intl.locale
+description: >
+    Checks the "firstDayOfWeek" property of the Locale prototype object.
+info: |
+    Intl.Locale.prototype.firstDayOfWeek
+
+    Unless specified otherwise in this document, the objects, functions, and constructors described in this standard are subject to the generic requirements and restrictions specified for standard built-in ECMAScript objects in the ECMAScript 2019 Language Specification, 10th edition, clause 17, or successor.
+
+    Every accessor property described in clauses 18 through 26 and in Annex B.2 has the attributes { [[Enumerable]]: false, [[Configurable]]: true } unless otherwise specified. If only a get accessor function is described, the set accessor function is the default value, undefined.
+includes: [propertyHelper.js]
+features: [Intl.Locale,Intl.Locale-info]
+---*/
+
+const propdesc = Object.getOwnPropertyDescriptor(Intl.Locale.prototype, "firstDayOfWeek");
+assert.sameValue(propdesc.set, undefined);
+assert.sameValue(typeof propdesc.get, "function");
+
+verifyProperty(Intl.Locale.prototype, "firstDayOfWeek", {
+  enumerable: false,
+  configurable: true,
+});
diff --git a/test/intl402/Locale/prototype/firstDayOfWeek/valid-id.js b/test/intl402/Locale/prototype/firstDayOfWeek/valid-id.js
new file mode 100644
index 0000000000..12acd526a9
--- /dev/null
+++ b/test/intl402/Locale/prototype/firstDayOfWeek/valid-id.js
@@ -0,0 +1,30 @@
+// Copyright 2023 Google Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-intl.locale
+description: >
+    Checks valid cases for the options argument to the Locale constructor.
+info: |
+    Intl.Locale.prototype.firstDayOfWeek
+    3. Return loc.[[FirstDayOfWeek]].
+
+features: [Intl.Locale,Intl.Locale-info]
+---*/
+
+const validIds = [
+  ["en-u-fw-mon", 1],
+  ["en-u-fw-tue", 2],
+  ["en-u-fw-wed", 3],
+  ["en-u-fw-thu", 4],
+  ["en-u-fw-fri", 5],
+  ["en-u-fw-sat", 6],
+  ["en-u-fw-sun", 7],
+];
+for (const [id, expected] of validIds) {
+  assert.sameValue(
+    new Intl.Locale(id).firstDayOfWeek,
+    expected,
+    `new Intl.Locale(${id}).firstDayOfWeek returns "${expected}"`
+  );
+}
diff --git a/test/intl402/Locale/prototype/firstDayOfWeek/valid-options.js b/test/intl402/Locale/prototype/firstDayOfWeek/valid-options.js
new file mode 100644
index 0000000000..6f1643afd2
--- /dev/null
+++ b/test/intl402/Locale/prototype/firstDayOfWeek/valid-options.js
@@ -0,0 +1,51 @@
+// Copyright 2023 Google Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-intl.locale
+description: >
+    Checks valid cases for the options argument to the Locale constructor.
+info: |
+    Intl.Locale.prototype.firstDayOfWeek
+    3. Return loc.[[FirstDayOfWeek]].
+
+features: [Intl.Locale,Intl.Locale-info]
+---*/
+
+const validFirstDayOfWeekOptions = [
+  ["mon", 1],
+  ["tue", 2],
+  ["wed", 3],
+  ["thu", 4],
+  ["fri", 5],
+  ["sat", 6],
+  ["sun", 7],
+  ["1", 1],
+  ["2", 2],
+  ["3", 3],
+  ["4", 4],
+  ["5", 5],
+  ["6", 6],
+  ["7", 7],
+  ["0", 7],
+  [1, 1],
+  [2, 2],
+  [3, 3],
+  [4, 4],
+  [5, 5],
+  [6, 6],
+  [7, 7],
+  [0, 7],
+];
+for (const [firstDayOfWeek, expected] of validFirstDayOfWeekOptions) {
+  assert.sameValue(
+    new Intl.Locale('en', { firstDayOfWeek }).firstDayOfWeek,
+    expected,
+    `new Intl.Locale("en", { firstDayOfWeek: ${firstDayOfWeek} }).firstDayOfWeek returns "${expected}"`
+  );
+  assert.sameValue(
+    new Intl.Locale('en-u-fw-WED', { firstDayOfWeek }).firstDayOfWeek,
+    expected,
+    `new Intl.Locale("en-u-fw-WED", { firstDayOfWeek: ${firstDayOfWeek} }).firstDayOfWeek returns "${expected}"`
+  );
+}
diff --git a/test/intl402/Locale/prototype/getWeekInfo/firstDay-by-id.js b/test/intl402/Locale/prototype/getWeekInfo/firstDay-by-id.js
new file mode 100644
index 0000000000..f5252e62ab
--- /dev/null
+++ b/test/intl402/Locale/prototype/getWeekInfo/firstDay-by-id.js
@@ -0,0 +1,31 @@
+// Copyright 2023 Google Inc. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-intl.locale.prototype.getWeekInfo
+description: >
+    Checks that the return value of Intl.Locale.prototype.getWeekInfo is an Object
+    with the correct keys and properties.
+info: |
+  get Intl.Locale.prototype.getWeekInfo
+  ...
+  6. Perform ! CreateDataPropertyOrThrow(info, "firstDay", wi.[[FirstDay]]).
+features: [Reflect,Intl.Locale,Intl.Locale-info]
+---*/
+
+const validFirstDayOfWeekIds = [
+  ["en-u-fw-mon", 1],
+  ["en-u-fw-tue", 2],
+  ["en-u-fw-wed", 3],
+  ["en-u-fw-thu", 4],
+  ["en-u-fw-fri", 5],
+  ["en-u-fw-sat", 6],
+  ["en-u-fw-sun", 7],
+];
+for (const [id, expected] of validFirstDayOfWeekIds) {
+  assert.sameValue(
+    new Intl.Locale(id).getWeekInfo().firstDay,
+    expected,
+    `new Intl.Locale(${id}).getWeekInfo().firstDay returns "${expected}"`
+  );
+}
diff --git a/test/intl402/Locale/prototype/getWeekInfo/firstDay-by-option.js b/test/intl402/Locale/prototype/getWeekInfo/firstDay-by-option.js
new file mode 100644
index 0000000000..bdf9cc280c
--- /dev/null
+++ b/test/intl402/Locale/prototype/getWeekInfo/firstDay-by-option.js
@@ -0,0 +1,52 @@
+// Copyright 2023 Google Inc. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-intl.locale.prototype.getWeekInfo
+description: >
+    Checks that the return value of Intl.Locale.prototype.getWeekInfo is an Object
+    with the correct keys and properties.
+info: |
+  get Intl.Locale.prototype.getWeekInfo
+  ...
+  6. Perform ! CreateDataPropertyOrThrow(info, "firstDay", wi.[[FirstDay]]).
+features: [Reflect,Intl.Locale,Intl.Locale-info]
+---*/
+
+const validFirstDayOfWeekOptions = [
+  ["mon", 1],
+  ["tue", 2],
+  ["wed", 3],
+  ["thu", 4],
+  ["fri", 5],
+  ["sat", 6],
+  ["sun", 7],
+  ["1", 1],
+  ["2", 2],
+  ["3", 3],
+  ["4", 4],
+  ["5", 5],
+  ["6", 6],
+  ["7", 7],
+  ["0", 7],
+  [1, 1],
+  [2, 2],
+  [3, 3],
+  [4, 4],
+  [5, 5],
+  [6, 6],
+  [7, 7],
+  [0, 7],
+];
+for (const [firstDayOfWeek, expected] of validFirstDayOfWeekOptions) {
+  assert.sameValue(
+    new Intl.Locale('en', { firstDayOfWeek }).getWeekInfo().firstDay,
+    expected,
+    `new Intl.Locale("en", { firstDayOfWeek: ${firstDayOfWeek} }).getWeekInfo().firstDay returns "${expected}"`
+  );
+  assert.sameValue(
+    new Intl.Locale('en-u-fw-WED', { firstDayOfWeek }).getWeekInfo().firstDay,
+    expected,
+    `new Intl.Locale("en-u-fw-WED", { firstDayOfWeek: ${firstDayOfWeek} }).firstDayOfWeek returns "${expected}"`
+  );
+}