Per app language settings not working on recent macOS versions

[sdassow]

Checklist

• I have searched the issue tracker for open issues that relate to the same problem, before opening a new one.
• This issue only relates to a single bug. I will open new issues for any other problems.

Describe the bug

In recent versions of macOS a language can be chosen per app. Fyne does not seem to support this yet, and in fact it does require support from the application.

How to reproduce

1. Install any Fyne app that supports more than one language
2. Go to SystemSettings -> General -> Language & Region -> Applications
3. Click "+" and select installed Fyne app

Screenshots

Example code

Any installed Fyne app shows this.

Fyne version

develop

Go compiler version

go1.23.3 darwin/amd64

Operating system and version

macOS Sonoma (14.7.1)

Additional Information

Simply creating lproj directories in Contents/Resources/ makes the languages appear, but when selected the app still doesn't localize. Maybe some additional API needs to be called?

The directory format for localization is mentioned here: https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFBundles/BundleTypes/BundleTypes.html

[sdassow]

Found something that seems related: tumic0/GPXSee#474
As I understand instead of the .lproj directories it can be done via plist: tumic0/GPXSee@2549204

[sdassow]

With both PRs referenced above applied it looks like the following in macOS settings, and the app gets the preference too:

[sdassow]

Sort of related, and maybe a useful keyword at some point in the future: CFBundleDevelopmentRegion