Add language option for users

[BerglundDaniel]

Add an option for users to select language. Then over time we can add English translations of the pages

• [ ] Add possibility for member to update language on member page
• [ ] Send the correct email based on language
• [ ] Add language to exported information so that we can use it in mailchimp and such
• [ ] Implement language support on the admin pages

[HalfVoxel]

The frontend automatically chooses the language based on the user's browser's preferred language now. However, there are currently no translations to any other language. So everything is still in English or Swedish, somewhat inconsistently. Swedish (or any other language) support can be added by editing the translations.tsx file. And all current hardcoded swedish strings should be defined using the translation system.

[BerglundDaniel]

Stripe customer object has _preferredlocales which might also be useful to update based on the members language

[kriffe]

Perhaps this also needs to adress how the primary language is stored? strings in code vs db or separate files, etc