Add Language option to General settings

[dstillman]

For users who run their OS in one language but still want Zotero in another (and to make it easier for us to verify other locales)

As on desktop, it should use the localized version of each language name. Can get the strings from here:

https://github.com/zotero/zotero/blob/main/chrome/content/zotero/xpcom/locale.js

[mvasilak]

@dstillman since we added localizations, in Settings.app > Apps > Zotero the Preferred Language option should appear.
We can look into adding an option in the app settings that mirrors the system one, if possible, or just provide an option that deep links to the system setting.