Add a language chooser

Closes #1015

What does this MR do?

Adds a "change language" to the user menu that opens a popup. After selecting a language, the page reloads and shows the chosen language. It is also permanently stored in fs_foodsaver and is not lost after a logout. This will make it more easy to use and test the translations (e.g. !1875 (merged) )

How confident are you it won't break things if deployed?

Very sure

How to test

Steps a reviewer can take to verify that this MR does what it says it does e.g.

1. Checkout branch locally
2. Login as foodsaver
3. Go to the user menu ("Dein Account") -> language chooser
4. Select a language and accept
5. The language should have changed. You can see that in the menu bar
6. Log out and log in again. The language should still be the same

Screenshots (if applicable)

Any relevant screenshots if this is a design / frontend change

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• use "state:" labels to track this MR's state until it was beta tested
• added an entry to CHANGELOG.md
• add a short text that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in Beta Testing Repo:
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...). how this change can be tested.
  • Be aware, that also non technical people should understand.

Release notes text

Über das Menü kannst du die Sprache der Webseite ändern.