Incorrect general long time pattern for some cultures on Android

[PopSlime]

Description

On Android, some cultures have an incorrect general long time pattern, causing DateTime.ToString(IFormatProvider) to produce badly formatted strings.

Reproduction Steps

Consider the following code:

new DateTime(2000, 1, 1, 20, 0, 0).ToString(new CultureInfo("zh-TW"));

Expected behavior

A correctly formatted string (like 2000/1/1 下午8:00:00) is returned.

Actual behavior

A badly formatted string 2000/1/1 8:00:00 is returned, in which a 12-hour clock is used without an AM/PM designator.

Regression?

No response

Known Workarounds

No response

Configuration

• .NET version: 8.0
• Target operating system: Android
• Architecture: x64, arm64
• Android version: 13 (tested both on an emulator and a physical device)

Other information

No response

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[PopSlime]

I did some further investigations, this issue seems to be device-dependent. Just in case, this issue was reproduced with the system-images;android-33;google_apis;x86_64 system image.

[tarekgh]

CC @vitek-karas @mkhamoyan @ilonatommy

[vitek-karas]

CC @matouskozak

[PopSlime]

This issue seems to relate to this ConvertIcuTimeFormatString method.

runtime/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs

Line 354 in b93061a

private static string ConvertIcuTimeFormatString(ReadOnlySpan<char> icuFormatString)

The current implementation does not cover the full Unicode Date Format Patterns. In the case of zh-TW (which expands to zh-Hant-TW and inherits zh-Hant,) the pattern symbol B is used [1], which is not covered in the aforementioned method.

Please consider supporting or partially supporting as many pattern symbols as possible just in case.

[1] https://github.com/unicode-org/cldr/blob/3147eda09f19de58463cc80d64248071531500a0/common/main/zh_Hant.xml#L4963

[PopSlime]

Related PR: unicode-org/cldr#1297

[PopSlime]

Affected CLDR version: 40 and above (https://cldr.unicode.org/index/downloads/cldr-40#h.mc372kkefa0z)

Affected Android version: 13 and above (https://developer.android.com/guide/topics/resources/internationalization#versioning-nougat)

[tarekgh]

@PopSlime thanks for the update. We should support the B conversion. Are you interested in submitting a PR for that?

CC @mkhamoyan

[PopSlime]

Hi, @tarekgh. I've submitted a PR for this issue but I'm not sure how to test it. Would you mind checking it out?