<i18n dev> RFR: 8369590: LocaleEnhanceTest has incorrectly passing test case [v2]

[Justin Lu]

On Mon, 13 Oct 2025 22:26:07 GMT, Naoto Sato <naoto at openjdk.org> wrote:

>> Justin Lu has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Adding test case to confirm duplicate U-extension attributes for setExtension(char, String)
>
> IIUC, the quote from the RFC refers to duplicate singletons. For example, it would reject something like `-u-aa-bbb-u-cc-ddd`. So I believe that rule doesn’t apply to cases like `-u-aa-bbb-AA-ccc`. I checked the `-u` extension definition in LDML but couldn’t find any description regarding duplicate keywords.
> 
> That said, I think it makes sense to allow them in lenient mode and throw an exception in strict mode. Since this would introduce a behavioral change, I’d expect it to require a CSR.

@naotoj CSR is filed and this PR is updated with the appropriate specification updates. `setExtension(char, String)` is also updated to align with `setLanguageTag(String)` on the behavior of duplicate U-extension keys and attributes as we discussed.

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PR Comment: https://git.openjdk.org/jdk/pull/27775#issuecomment-3403621489