Filter comments taking into account the current content language

WIP: This would filter comments per language.

If we have a thread, and the root comment is not translated but the responses are, there are weird identations as the first won't be shown.
It would be great checking how D7 worked in that scenario.

Scenario: node translated in English and Spanish

Add comment 1. in English
Add comment 1.1 in Spanish
Add comment 2 in English
Translate comment 2 to Spanish
Add comment 3 in Spanish

In English I should see:

1
2

In Spanish I should see:
1.2? Not sure. Also not sure if it's good enough if it has the wrong identation as probably it's not a very common scenario.
2
3

Accidentally uploaded empty patch.

Fixing a minor CCF error to make #29 pass the test.

Since this is adding a new configuration option it will need an upgrade path for existing sites. With test coverage.

Next step is not adding tests or upgrade path, but decide if this is something we want to do and if patch at #28 is good enough.

A screenshot of how does it look in D7 when we have an scenario like the described in #28 would be helpful.

I'll attach screenshots of how it looks like in D10.1 with that patch if noone beats me to do it.

Gotcha

Never put thought into it but wonder how most sites (non Drupal) handle comments in different languages.

If an article is posted wouldn’t someone like to see all comments vs maybe the comments just in my language.

But can see the other side of if majority of comments are in another language may not be useful.

Just thinking out loud