Add translations for keyboard layouts.

[demiankatz]

@ThoWagen, I know that we had previously discussed aliasing keyboard layouts to language codes to accomplish translations, but when I started investigating the possibility, I discovered some significant semantic differences. While there is a lot of overlap, in some cases the layouts correspond to region names rather than language names, or there are multiple layouts for the same language. Thus, I think we'll have better control if we give the layouts their own text domain. This PR adds the text domain, adjusts the template to use it, and fixes an invalid layout name in one of the configuration examples.

Translations are not 100% complete -- we might be able to fill in a few more as further progress is made on #3200 -- but I think this is at least a strong starting point.

TODO

• Update to use aliasing where appropriate after Add ISO 639-3 language code translations. #3200 is merged

[ThoWagen]

Would it be possible to allow aliasing into other text domains so that we could add an alias.ini in KeyboardLayout and use it for the layouts that are language names? Then we could add e.g. german = ISO639-3::deu. But maybe that would make things more complicated rather than easier. I don't think that your approach in #3249 supports aliasing into other text domains and it would probably not be straight forward to implement. So this is just an idea.

[demiankatz]

@ThoWagen, I'll address the idea of aliasing into other TextDomains on #3249 shortly, since I think that's probably the best place to have that conversation.

However, if we decide that it is not practical to directly alias across TextDomains, we could still accomplish the same effect here by making these language files inherit from the equivalent ISO639-3 TextDomains and then defining the aliases locally. This would use more cache space/memory because it would duplicate all the translations, but it would allow us to reduce language file maintenance.

I'll leave this open until we resolve this issue one way or the other.

[demiankatz]

@ThoWagen, I have reimplemented this using the new aliasing mechanism, and it seems to be working correctly. I believe it is now ready for your review.

[ThoWagen]

This looks good to me :)

Only one small hint: I'm not sure if it is intended or not that "farsi" is aliased as "ISO639-3::per" but also translated as "Farsi" in en.ini.

[demiankatz]

Thanks, @ThoWagen! Regarding your observation, it was intentional (I thought it might be better to keep the translation closer to the code when choosing between two synonyms for the language), but in retrospect, I don't think it's necessary, and it might actually be more confusing, so I'll remove the override and just keep the alias.