In T422440: figure out if we're still using internationalization/localization, we verified that this repo is still getting translated upstream, and that you can set your language using a cookie.

This ticket is to add a dropdown language picker in the Preferences panel, so that users can change languages easily. Right now zero users know about the cookie so they basically can't change languages, but the pieces are all there except the language picker.

• add a Vue component that is a language picker, in the preferences panel. it needs to load a list of languages in a dropdown menu.
• when the user saves, it needs to set the cookie (TsIntuition_userlang, with values such as en, es, etc.), then either change the language in a Vue-ish manner by changing a variable somewhere and everything automatically updates, or simply refresh the page for the user
• auto-detect the user's browser language, and set that as the default on first visit (i.e. if no cookie is set, set a cookie to that language)

Hint: The software that writes the language files to our repo is called Intuition. There's more info about it at https://github.com/CurbSafeCharmer/refill/blob/master/messages/README.md and https://github.com/Krinkle/intuition.

Hint: To get a list of languages for the dropdown, I think banana-i18n will have that in a variable somewhere. I imagine that library reads our /messages/ directory and parses all those message files.