Add locale picker to header

[nscuro]

Description

Adds a locale picker to the header of the page, next to the profile icon.

This is to make it easier to switch languages, without having to fiddle with browser settings.

Addressed Issue

N/A

Additional Details

Current version (don't ask me why the GIF quality is worse, no idea):

Original version:

Checklist

• I have read and understand the contributing guidelines
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[nscuro]

@fnxpt Fancy giving this a review?

Besides the code itself, please have a look at the new translations. For German, the auto-translate suggested "polieren" for "Polish" (as in polishing, the verb lol).

[fnxpt]

As an additional comment, I would add flags instead of text, usually on these types of selectors its more common to see a flag

[nscuro]

Thanks @fnxpt!

I would add flags instead of text, usually on these types of selectors its more common to see a flag

Good point. I briefly looked into that but couldn't be bothered to add yet another NPM package just for flag icons. I'll have another look, I agree that country codes might be sub-optimal.

[fnxpt]

Good point. I briefly looked into that but couldn't be bothered to add yet another NPM package just for flag icons. I'll have another look, I agree that country codes might be sub-optimal.

We can also add the images on the resources and just do {locale}.png, no need for an extra library

[nscuro]

@fnxpt Any good source for flag icons you can recommend?

[nscuro]

Languages are now displayed as country flag emojis instead of language codes, as per @fnxpt's suggestion:

Got feedback from @msymons that the picker should probably be located closer to the user profile. I'll see if I can add it to the dropdown that opens when clicking the user icon.

[nscuro]

@fnxpt Suggestions applied. Updated the GIF in the PR description to show the current look&feel of the language picker. Can you have another look please?

[fnxpt]

lgtm