Clean JS files for case-insensitive file systems

[heyanlong]

When installing in case-insensitive operating systems, such as WSL2 and macOS, the case of the JS language file will be considered to be one file, and composer will cause an error.

[sampoyigi]

Can you add some description of what issue this is solving?

[ObjectBoxPC]

(Note: I am new to this codebase so my understanding of the situation may be incomplete.)

In this directory there appear to be "duplicate" locale files, some that use capital letters for the country code (for example "en-AU") and some that use lowercase letters ("en-au"). Files whose names differ only in letter case can cause problems on case-insensitive filenames. Besides that, they are confusing because it's not clear which one is actually being used for the given locale.

These appear to have been introduced in commit 415499e .

[sampoyigi]

Thank you!