Add a language toggle

[Seraphiana]

Stonecutter should have a language toggle so that users can change the language to differ from the language that their browser runs in.

This toggle should be visible on all pages, and should use a cookie to set the language if the user is not logged in, or should add a variable to the user's profile if they are logged in.

These variables should be preferentially used by the translations that are already implemented, before defaulting back to the browser's language