diff --git a/test/staging/Intl402/Temporal/old/date-toLocaleString.js b/test/staging/Intl402/Temporal/old/date-toLocaleString.js
index 8a046815c4..282b22850e 100644
--- a/test/staging/Intl402/Temporal/old/date-toLocaleString.js
+++ b/test/staging/Intl402/Temporal/old/date-toLocaleString.js
@@ -21,16 +21,16 @@ function maybeGetWeekdayOnlyFormat() {
 }
 
 var date = Temporal.PlainDate.from("1976-11-18T15:23:30");
-assert.sameValue(`${ date.toLocaleString("en", { timeZone: "America/New_York" }) }`, "11/18/1976")
-assert.sameValue(`${ date.toLocaleString("de", { timeZone: "Europe/Vienna" }) }`, "18.11.1976")
+assert.sameValue(`${ date.toLocaleString("en-US", { timeZone: "America/New_York" }) }`, "11/18/1976");
+assert.sameValue(`${ date.toLocaleString("de-AT", { timeZone: "Europe/Vienna" }) }`, "18.11.1976");
 var fmt = maybeGetWeekdayOnlyFormat();
 if (fmt) assert.sameValue(fmt.format(date), "Thursday");
 
 // should ignore units not in the data type
-assert.sameValue(date.toLocaleString("en", { timeZoneName: "long" }), "11/18/1976");
-assert.sameValue(date.toLocaleString("en", { hour: "numeric" }), "11/18/1976");
-assert.sameValue(date.toLocaleString("en", { minute: "numeric" }), "11/18/1976");
-assert.sameValue(date.toLocaleString("en", { second: "numeric" }), "11/18/1976");
+assert.sameValue(date.toLocaleString("en-US", { timeZoneName: "long" }), "11/18/1976");
+assert.sameValue(date.toLocaleString("en-US", { hour: "numeric" }), "11/18/1976");
+assert.sameValue(date.toLocaleString("en-US", { minute: "numeric" }), "11/18/1976");
+assert.sameValue(date.toLocaleString("en-US", { second: "numeric" }), "11/18/1976");
 
 // works when the object's calendar is the same as the locale's calendar
 var d = Temporal.PlainDate.from({
diff --git a/test/staging/Intl402/Temporal/old/datetime-toLocaleString.js b/test/staging/Intl402/Temporal/old/datetime-toLocaleString.js
index 3d041f2c6a..ee88de87bc 100644
--- a/test/staging/Intl402/Temporal/old/datetime-toLocaleString.js
+++ b/test/staging/Intl402/Temporal/old/datetime-toLocaleString.js
@@ -8,7 +8,7 @@ features: [Temporal]
 ---*/
 
 function maybeGetWeekdayOnlyFormat() {
-  const fmt = new Intl.DateTimeFormat("en", { weekday: "long", timeZone: "Europe/Vienna" });
+  const fmt = new Intl.DateTimeFormat("en-US", { weekday: "long", timeZone: "Europe/Vienna" });
   if (
     ["era", "year", "month", "day", "hour", "minute", "second", "timeZoneName"].some(
       (prop) => prop in fmt.resolvedOptions()
@@ -21,17 +21,17 @@ function maybeGetWeekdayOnlyFormat() {
 }
 
 var datetime = Temporal.PlainDateTime.from("1976-11-18T15:23:30");
-assert.sameValue(`${datetime.toLocaleString("en", { timeZone: "America/New_York" })}`, "11/18/1976, 3:23:30 PM");
-assert.sameValue(`${datetime.toLocaleString("de", { timeZone: "Europe/Vienna" })}`, "18.11.1976, 15:23:30");
+assert.sameValue(`${datetime.toLocaleString("en-US", { timeZone: "America/New_York" })}`, "11/18/1976, 3:23:30 PM");
+assert.sameValue(`${datetime.toLocaleString("de-AT", { timeZone: "Europe/Vienna" })}`, "18.11.1976, 15:23:30");
 var fmt = maybeGetWeekdayOnlyFormat();
 if (fmt) assert.sameValue(fmt.format(datetime), "Thursday");
 
 // should ignore units not in the data type
-assert.sameValue(datetime.toLocaleString("en", { timeZoneName: "long" }), "11/18/1976, 3:23:30 PM");
+assert.sameValue(datetime.toLocaleString("en-US", { timeZoneName: "long" }), "11/18/1976, 3:23:30 PM");
 
 // should use compatible disambiguation option
 var dstStart = new Temporal.PlainDateTime(2020, 3, 8, 2, 30);
-assert.sameValue(`${dstStart.toLocaleString("en", { timeZone: "America/Los_Angeles" })}`, "3/8/2020, 3:30:00 AM");
+assert.sameValue(`${dstStart.toLocaleString("en-US", { timeZone: "America/Los_Angeles" })}`, "3/8/2020, 3:30:00 AM");
 
 // works when the object's calendar is the same as the locale's calendar
 var dt = Temporal.PlainDateTime.from({
diff --git a/test/staging/Intl402/Temporal/old/instant-toLocaleString.js b/test/staging/Intl402/Temporal/old/instant-toLocaleString.js
index 07f4e3c889..d7b92c7998 100644
--- a/test/staging/Intl402/Temporal/old/instant-toLocaleString.js
+++ b/test/staging/Intl402/Temporal/old/instant-toLocaleString.js
@@ -8,7 +8,7 @@ features: [Temporal]
 ---*/
 
 function maybeGetWeekdayOnlyFormat() {
-  const fmt = new Intl.DateTimeFormat("en", { weekday: "long", timeZone: "Europe/Vienna" });
+  const fmt = new Intl.DateTimeFormat("en-US", { weekday: "long", timeZone: "Europe/Vienna" });
   if (
     ["era", "year", "month", "day", "hour", "minute", "second", "timeZoneName"].some(
       (prop) => prop in fmt.resolvedOptions()
@@ -21,13 +21,13 @@ function maybeGetWeekdayOnlyFormat() {
 }
 
 var instant = Temporal.Instant.from("1976-11-18T14:23:30Z");
-assert.sameValue(`${instant.toLocaleString("en", { timeZone: "America/New_York" })}`, "11/18/1976, 9:23:30 AM");
-assert.sameValue(`${instant.toLocaleString("de", { timeZone: "Europe/Vienna" })}`, "18.11.1976, 15:23:30");
+assert.sameValue(`${instant.toLocaleString("en-US", { timeZone: "America/New_York" })}`, "11/18/1976, 9:23:30 AM");
+assert.sameValue(`${instant.toLocaleString("de-AT", { timeZone: "Europe/Vienna" })}`, "18.11.1976, 15:23:30");
 var fmt = maybeGetWeekdayOnlyFormat();
 if (fmt) assert.sameValue(fmt.format(instant), "Thursday");
 
 // outputs timeZoneName if requested
-var str = instant.toLocaleString("en", {
+var str = instant.toLocaleString("en-US", {
   timeZone: "America/New_York",
   timeZoneName: "short"
 });
diff --git a/test/staging/Intl402/Temporal/old/monthday-toLocaleString.js b/test/staging/Intl402/Temporal/old/monthday-toLocaleString.js
index 208b1ec6ef..d064ef2736 100644
--- a/test/staging/Intl402/Temporal/old/monthday-toLocaleString.js
+++ b/test/staging/Intl402/Temporal/old/monthday-toLocaleString.js
@@ -7,25 +7,25 @@ description: monthday.toLocaleString()
 features: [Temporal]
 ---*/
 
-var calendar = new Intl.DateTimeFormat("en").resolvedOptions().calendar;
+var calendar = new Intl.DateTimeFormat("en-US").resolvedOptions().calendar;
 var monthday = Temporal.PlainMonthDay.from({
   monthCode: "M11",
   day: 18,
   calendar
 });
-assert.sameValue(`${ monthday.toLocaleString("en", { timeZone: "America/New_York" }) }`, "11/18")
-assert.sameValue(`${ monthday.toLocaleString("de", {
+assert.sameValue(`${ monthday.toLocaleString("en-US", { timeZone: "America/New_York" }) }`, "11/18");
+assert.sameValue(`${ monthday.toLocaleString("de-AT", {
   timeZone: "Europe/Vienna",
   calendar
-}) }`, "18.11.")
+}) }`, "18.11.");
 
 // should ignore units not in the data type
-assert.sameValue(monthday.toLocaleString("en", { timeZoneName: "long" }), "11/18");
-assert.sameValue(monthday.toLocaleString("en", { year: "numeric" }), "11/18");
-assert.sameValue(monthday.toLocaleString("en", { hour: "numeric" }), "11/18");
-assert.sameValue(monthday.toLocaleString("en", { minute: "numeric" }), "11/18");
-assert.sameValue(monthday.toLocaleString("en", { second: "numeric" }), "11/18");
-assert.sameValue(monthday.toLocaleString("en", { weekday: "long" }), "11/18");
+assert.sameValue(monthday.toLocaleString("en-US", { timeZoneName: "long" }), "11/18");
+assert.sameValue(monthday.toLocaleString("en-US", { year: "numeric" }), "11/18");
+assert.sameValue(monthday.toLocaleString("en-US", { hour: "numeric" }), "11/18");
+assert.sameValue(monthday.toLocaleString("en-US", { minute: "numeric" }), "11/18");
+assert.sameValue(monthday.toLocaleString("en-US", { second: "numeric" }), "11/18");
+assert.sameValue(monthday.toLocaleString("en-US", { weekday: "long" }), "11/18");
 
 // works when the object's calendar is the same as the locale's calendar
 var md = Temporal.PlainMonthDay.from({
diff --git a/test/staging/Intl402/Temporal/old/time-toLocaleString.js b/test/staging/Intl402/Temporal/old/time-toLocaleString.js
index ff18d3d6e0..331dccc74f 100644
--- a/test/staging/Intl402/Temporal/old/time-toLocaleString.js
+++ b/test/staging/Intl402/Temporal/old/time-toLocaleString.js
@@ -8,12 +8,12 @@ features: [Temporal]
 ---*/
 
 var time = Temporal.PlainTime.from("1976-11-18T15:23:30");
-assert.sameValue(`${time.toLocaleString("en", { timeZone: "America/New_York" })}`, "3:23:30 PM");
-assert.sameValue(`${time.toLocaleString("de", { timeZone: "Europe/Vienna" })}`, "15:23:30");
+assert.sameValue(`${time.toLocaleString("en-US", { timeZone: "America/New_York" })}`, "3:23:30 PM");
+assert.sameValue(`${time.toLocaleString("de-AT", { timeZone: "Europe/Vienna" })}`, "15:23:30");
 
 // should ignore units not in the data type
-assert.sameValue(time.toLocaleString("en", { timeZoneName: "long" }), "3:23:30 PM");
-assert.sameValue(time.toLocaleString("en", { year: "numeric" }), "3:23:30 PM");
-assert.sameValue(time.toLocaleString("en", { month: "numeric" }), "3:23:30 PM");
-assert.sameValue(time.toLocaleString("en", { day: "numeric" }), "3:23:30 PM");
-assert.sameValue(time.toLocaleString("en", { weekday: "long" }), "3:23:30 PM");
+assert.sameValue(time.toLocaleString("en-US", { timeZoneName: "long" }), "3:23:30 PM");
+assert.sameValue(time.toLocaleString("en-US", { year: "numeric" }), "3:23:30 PM");
+assert.sameValue(time.toLocaleString("en-US", { month: "numeric" }), "3:23:30 PM");
+assert.sameValue(time.toLocaleString("en-US", { day: "numeric" }), "3:23:30 PM");
+assert.sameValue(time.toLocaleString("en-US", { weekday: "long" }), "3:23:30 PM");
diff --git a/test/staging/Intl402/Temporal/old/yearmonth-toLocaleString.js b/test/staging/Intl402/Temporal/old/yearmonth-toLocaleString.js
index fdc1c6d217..f9192ca4b2 100644
--- a/test/staging/Intl402/Temporal/old/yearmonth-toLocaleString.js
+++ b/test/staging/Intl402/Temporal/old/yearmonth-toLocaleString.js
@@ -7,15 +7,15 @@ description: yearmonth.toLocaleString()
 features: [Temporal]
 ---*/
 
-var calendar = new Intl.DateTimeFormat("en").resolvedOptions().calendar;
+var calendar = new Intl.DateTimeFormat("en-US").resolvedOptions().calendar;
 var yearmonth = Temporal.PlainYearMonth.from({
   year: 1976,
   month: 11,
   calendar
 });
-assert.sameValue(`${yearmonth.toLocaleString("en", { timeZone: "America/New_York" })}`, "11/1976");
+assert.sameValue(`${yearmonth.toLocaleString("en-US", { timeZone: "America/New_York" })}`, "11/1976");
 assert.sameValue(
-  `${yearmonth.toLocaleString("de", {
+  `${yearmonth.toLocaleString("de-AT", {
     timeZone: "Europe/Vienna",
     calendar
   })}`,
@@ -23,12 +23,12 @@ assert.sameValue(
 );
 
 // should ignore units not in the data type
-assert.sameValue(yearmonth.toLocaleString("en", { timeZoneName: "long" }), "11/1976");
-assert.sameValue(yearmonth.toLocaleString("en", { day: "numeric" }), "11/1976");
-assert.sameValue(yearmonth.toLocaleString("en", { hour: "numeric" }), "11/1976");
-assert.sameValue(yearmonth.toLocaleString("en", { minute: "numeric" }), "11/1976");
-assert.sameValue(yearmonth.toLocaleString("en", { second: "numeric" }), "11/1976");
-assert.sameValue(yearmonth.toLocaleString("en", { weekday: "long" }), "11/1976");
+assert.sameValue(yearmonth.toLocaleString("en-US", { timeZoneName: "long" }), "11/1976");
+assert.sameValue(yearmonth.toLocaleString("en-US", { day: "numeric" }), "11/1976");
+assert.sameValue(yearmonth.toLocaleString("en-US", { hour: "numeric" }), "11/1976");
+assert.sameValue(yearmonth.toLocaleString("en-US", { minute: "numeric" }), "11/1976");
+assert.sameValue(yearmonth.toLocaleString("en-US", { second: "numeric" }), "11/1976");
+assert.sameValue(yearmonth.toLocaleString("en-US", { weekday: "long" }), "11/1976");
 
 // works when the object's calendar is the same as the locale's calendar
 var ym = Temporal.PlainYearMonth.from({
diff --git a/test/staging/Intl402/Temporal/old/zoneddatetime-toLocaleString.js b/test/staging/Intl402/Temporal/old/zoneddatetime-toLocaleString.js
index 6fe83aca53..39d6fea936 100644
--- a/test/staging/Intl402/Temporal/old/zoneddatetime-toLocaleString.js
+++ b/test/staging/Intl402/Temporal/old/zoneddatetime-toLocaleString.js
@@ -8,7 +8,7 @@ features: [Temporal]
 ---*/
 
 function maybeGetWeekdayOnlyFormat() {
-  const fmt = new Intl.DateTimeFormat("en", { weekday: "long", timeZone: "Europe/Vienna" });
+  const fmt = new Intl.DateTimeFormat("en-US", { weekday: "long", timeZone: "Europe/Vienna" });
   if (
     ["era", "year", "month", "day", "hour", "minute", "second", "timeZoneName"].some(
       (prop) => prop in fmt.resolvedOptions()
@@ -21,23 +21,23 @@ function maybeGetWeekdayOnlyFormat() {
 }
 
 var zdt = Temporal.ZonedDateTime.from("1976-11-18T15:23:30+01:00[Europe/Vienna]");
-assert.sameValue(zdt.toLocaleString("en"), "11/18/1976, 3:23:30 PM GMT+1");
-assert.sameValue(zdt.toLocaleString("de"), "18.11.1976, 15:23:30 MEZ");
+assert.sameValue(zdt.toLocaleString("en-US"), "11/18/1976, 3:23:30 PM GMT+1");
+assert.sameValue(zdt.toLocaleString("de-AT"), "18.11.1976, 15:23:30 MEZ");
 
 const fmt = maybeGetWeekdayOnlyFormat();
 // uses only the options in resolvedOptions
 if (fmt) assert.sameValue(fmt.format(zdt), "Thursday");
 // can override the style of the time zone name
 assert.sameValue(
-  zdt.toLocaleString("en", { timeZoneName: "long" }),
+  zdt.toLocaleString("en-US", { timeZoneName: "long" }),
   "11/18/1976, 3:23:30 PM Central European Standard Time"
 );
 
 // works if the time zone given in options agrees with the object's time zone
-assert.sameValue(zdt.toLocaleString("en", { timeZone: "Europe/Vienna" }), "11/18/1976, 3:23:30 PM GMT+1");
+assert.sameValue(zdt.toLocaleString("en-US", { timeZone: "Europe/Vienna" }), "11/18/1976, 3:23:30 PM GMT+1");
 
 // throws if the time zone given in options disagrees with the object's time zone
-assert.throws(RangeError, () => zdt.toLocaleString("en", { timeZone: "America/New_York" }));
+assert.throws(RangeError, () => zdt.toLocaleString("en-US", { timeZone: "America/New_York" }));
 
 // works when the object's calendar is the same as the locale's calendar
 var zdt = new Temporal.ZonedDateTime(0n, "UTC", "japanese");