Add document locale support

[F0rgenet]

Adds possibility to use

#set text(lang: "fr")

I used this file to determine all supported languages:
https://github.com/typst/typst/blob/main/crates/typst-library/src/text/lang.rs

Users can still use local-names argument to provide additional translations/customization (it will be prioritized), this PR is backwards compatible

This one needs attention, maybe it could be done better than i did

Closes #47

[F0rgenet]

I have rebased this branch on main (with previous commits), it seems that github doesn't care about PRs that depend on each other, maybe if you will merge previous, this PR will add only one commit

[F0rgenet]

I also suggest option in repo settings when PRs need approval only for new contributors

[Mc-Zen]

Actually it is already set to Require approval for first-time contributors but only now after I merged your former PR, GitHub considers you a not-first-time contributor I guess.

[F0rgenet]

Also, feel free to correct my wording — im not a native English speaker. I understand English better than I speak it, so I might make some mistakes here and there

For the same reason, I would prefer not to write a documentation block for this feature if you decide to merge it :)

[F0rgenet]

And should we update custom-style.typ in funny-math example? Should custom styles respect multiple languages?

[Mc-Zen]

Hi, I'm sorry that I'm only now getting back to your PR but I had some other important duties this week.

I like the idea and would like to adopt this feature but I have one or two suggestions.

• Let us make the parameter local-names of show-module default to auto. auto means "use the language currently set with the predefined translations".
• I also think that partial overrides would make sense if the user only does not like the word for "variables" for example.

I will add a commit to address these points.

[Mc-Zen]

Later, with custom types, translations could be solved much easier and more natively I think but that's a story for a future time.

[Mc-Zen]

Thank you!

[Mc-Zen]

I just released an update with the new feature included. It should be on Typst Universe by the start of the next week :)