Reintroduce the language selector in the Drupal CMS installer

So, here's the thing...

Drupal CMS's installer is now based on the Recipe Installer Kit → framework, which is probably where most of these changes need to actually happen.

For now, go ahead and implement it in Drupal CMS however you see fit -- let's just get something that works. Once it's ready to be committed, we can move the parts into Recipe Installer Kit as needed.

I think we probably need to move this to Recipe Installer Kit, since that's where all the installer's functional code exists.

We'll also need to research where, exactly, the translations are loaded from.

Hi @phenaproxima

Though I understand about having the functionality in the Recipe Installer Kit, it looks like we'll be needing some theming, css, js too, which should be on this project, right? so maybe it makes sense to have one issue for each (?)

About downloading the translations, I think we can reuse all of Drupal core features and infrastructure for that so the only thing we need to worry about is how this project is parsed and uploaded to localize.drupal.org. I'll follow up about this on other issues.

@jose reyero, the translating is a bit tricky because a lot of the new, untranslated strings come from the installer's custom theme, which is, well, a custom theme and not a standalone project.

Does it need to be moved into its own project for this to work?

It looks like most of the strings will just be parsed treating this project like a generic folder. Trying with the potx module...

drush potx --folder=temp/drupal_cms

------- --------- 
  Files   Strings  
 ------- --------- 
  461     31       
 ------- --------- 

However, since which files are extracted depend on the potx module, we can add patches for that one too in case it is needed, like this one ✨ Extract strings from Recipes Active
So I'd suggest we move on and address the issue later if there are missing strings

(Attached the extracted strings).