The translation of microbit.org is kindly developed by our community. You can find out more about it at microbit.org/translate.
The translations are hosted using a service called Crowdin and we have published guidance on translating microbit.org. Crowdin also has an introductory tutorial if you are interested in getting started.
Translations for video subtitles are coordinated using a third-party tool called Amara. You can find out more about the process in this support article.
You can also localise your MakeCode extensions if you are creating one for an accessory.