Fix issues to deploy /lang directory as-is in production

[stephanegigandet]

This is a meta-bug to identify issues that need to be fixed if we want to deploy the /lang directory as-is in production, instead of hand picking files and copying them manually.

1. Bad translations / Outdated translations

Texts have been translated in 2 ways:

• Historically, using pages on OFF wikis. Those translations are very good, but they may be old.
• Through crowdin, from the English text. Some of those translations are quite bad (meaning you see them and you cringe).

Going forward, we probably need to standardize on using Crowdin for texts translation (as it's easier to update parts of the translations), but we first need to review the texts in OFF main languages.

e.g. compare those 2 pages:

• https://fr.openfoodfacts.org/decouvrir (currently in production, original translation on the wiki)
• https://fr.openfoodfacts.org/discover (translation from English through Crowdin)

2. Broken links

The URLs of some pages in some languages have been translated. E.g. the /discover page is /decouvrir in French.

Some of those pages with translated names are in github (e.g. for French), but most are not (e.g. for German, in production, there are many files with translated names in /srv/off/lang/de/texts that are not in github). Some are in github but are broken (e.g. https://es.openfoodfacts.org/contribuir is a copy of the /descubrir text).

Proposed solution: remove files with translated names from github (once we have fixed the bad translations from the first item above), and implement #1818 so that we can keep translated URLs.

[stephanegigandet]

I deployed the master branch, with the /lang directory on the dev server:
https://uk.openfoodfacts.dev
https://es.openfoodfacts.dev
https://de.openfoodfacts.dev
https://it.openfoodfacts.dev

[teolemon]

I started porting your (better) translations to Crowdin.

[teolemon]

#2831 is adding variables to the config files so that we can remove language dependant images, urls and often changing numbers from the files.
This reduces risk of bad translations, and reduces retranslations.

[github-actions]

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