[Plan] Comment module major multilingual issues

Problem/Motivation

I'm opening this issue here to raise focus on the subject as all the other similar bugs that are filed 1. are not concentrated somewhere, 2. are 4 years old without major progress 3. none of them has made enough impression to show to the community how important they are.

The comment module at the moment for a multilingual Drupal 8/9 site is completely useless. I'm developing a site the last weeks and I hit a wall the moment I started testing the comments. According to the existing solutions we should hack the core and the suggested solutions address only a fraction of the problems. It makes me great surprise how the developers/maintainers of drupal core are proudly moving to D9 when such important issues aren't even solved in D8!!

So let's present here the major problems the comment module is currently having:
1. Not able to filter comments per language
2. If you write a comment in a translated page you get redirected to the non-translated page when you save
3. Previewing a comment is not working if you are in a translated page (white screen of death)
4. Deletion of a comment in a translated page redirects you back to the non-translated one
5. Number of comments shows the sum for all languages not the ones corresponding to the current language (this should be addressed together with 1.). Also this sum is shown only in the non translated page. In the translated page no counter is shown.
6. Removing title from comments without changing twig files. Other frameworks have no title in comments so this should be an option.
7. Permalinks sometimes include the language code and sometimes not, often leading to "page not found" errors. Node comments behave differently compared to Forum comments regarding language code in permalinks.

How proud should we be for the multilingual capabilities of Drupal if the above really basic functionality is not available? Personally, I selected Drupal for my last project exactly because I was believing that would be really powerful for a multilingual site, but now I'm stuck and I'm forced to use another framework. All my work is now gone...

Steps to reproduce

Install a new D8/D9
Enable multilingual
Enable another language
Make an article and a translation of it.
Try to write, preview and delete comments in the translated article.

Proposed resolution

The maintainers should focus on this and solve the issues as this module is in the core and most of the solutions currently require hacking the core. I consider this major issue and really basic and important functionality.

Similar topics

#2751269: Submitting a comment in the non default language redirects you to the default language -> 4,5 years old. Addresses only No.2 by hacking the core

#2751267: Comments are not filtered on language -> 4.5 years old. Simple solution without core patch is #38 but not reliable and not a real solution. Patch #33 is a real solution but there are still issues with permalinks in translated pages and the sum of comments is not calculated per language.

#3145146: On the translated node the comment preview functionality is not working -> 0.5 years old. No answer whatsoever

Personally I gave up hope when I realized that the community the last 4.5 years has not solved these. As my last action before surrendering is this post here with the hope to raise awareness! Let's hope for the best. I really love drupal and it's really hard to give up on it...