Internationalization base

[Talanor]

Say hello to our lord and savior: internationalization.

This is stable on my staging environment, but probably not production ready.
I'm mainly opening this for tracking purposes / discussion and feedback from users / maintainers (and to move on with my life).

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Main points of contention :

• Created a user Model, which will be useful and needed for future features, even though my deployment from testing to staging was smooth, can't guarantee it for other users since it alters the db in a non trivial way.
• Django makemessages doesn't like manually tracked translations, but it also doesn't translate JS embedded in html templates. When running manage.py makemessages -a -d djangojs, it will comment out those translations. You can grep #~ in .po files and delete it to uncomment them before manage.py compilemessages
• I'm not entirely happy with some translations including HTML, but languages are tricky and I don't see a way around that as of right now. Someone more knowledgeable will be needed in the long run.
• Some translation blocks are not consistent (translating chunks vs translating the whole block with html) accross files. Not a major problem but not great.
• A HOW_TO_translators.md should be added to explain the steps (even though it is well documented on django's doc)

Edit: Most FR translations were AI generated. Even though I reviewed most of it, some weird stuff might have escaped me.

[yogeshojha]

Looks interesting, Thank you for the PR
which all languages are currently suppoted @Talanor ?

[Talanor]

A few fixes are still needed, I'll get to them when I can.

But for now only french and english.
Any language can be added by copy/pasting the locale/**/en/django.po and locale/**/en/djangojs.po, editing them accordingly, relaunching makemessages and compilemessages.

[yogeshojha]

Thank you, I think FR, ES and EN would be a very good start.
Thank you again for initiating a great effort.

If there are some bugs to be fixed, do you mind keeping this MR in DRAFT please?

@Talanor

[Talanor]

Ready for review / critiques / comments

[Talanor]

Hey, regarding the push to 2.2.0, considering it's been 7 months since the last release (2.0 vs 2.1), I can't help but feel this PR will be discontinued and have to go through tremendous work to merge by then.