doc: Add i18n support

[lilvinz]

• Enable Sphinx i18n configuration with UUID-based message IDs
• Add German (de) translation infrastructure
• Update documentation with translation workflow in CONTRIBUTING.md
• Configure .gitignore for translation artifacts

Consider this to be a proof of concept.

By now i am aware of pybricks/support#1345 but at least wanted to put this up for comments.

[dlech]

Looks like a nice start. I'm not sure if we have the bandwidth to take on translations right at this moment, but when we do, I think, that starting with the docs would be a good place to start to help us establish how we want to manage translations in general, e.g. using an external service to help manage it or not. It's much easier to push out updated docs outside of the Pybricks Code app so that can really speed up the development/feedback cycle.

One thing I can see a need for here is to be able to add some annotations to give hints to translators on things like Restructured Text formatting that needs to be preserved and when words are Python identifiers that should not be translated.

Also, it looks like this is just pulling strings from the .rst files and not any of the doc comments from .py files. How hard will it be to add that?

[lilvinz]

I have added a possible solution regarding the code comments using a sphinx-plugin.

In regard to translators and workflow i think a lot can nowadays been achieved via LLMs. All the example translations i did so far was via Claude 3.5 and as a German native speaker i can say they are absolutely usable even without manual reworking.

Doing the rest in the same way is a matter of a few hours.

In general what i am looking for the most is a translation of the blocks - because thats what my kids are dealing with primarily.