[Idea] Automatically mark translations as done

Currently adding new translations involves creating a checklist with all the supported languages and marking it as done after a PR has been merged. This has a few drawbacks:

• the PR reviewer has to manually go to given issue and the language as done
• the PR creator has to make sure he/she points to an issue
• some issues are already translated but they are not marked as done

I'm wondering if this could be automatized. After a translation would be added to given language on master branch a script should go through all issues and mark them as done. If all translations are done it should be closed.

This involves probably some changes in the issue formatting and/or creating one issue per translation but maybe(?) it could be done and would be a nice quality of life improvement.

Start by reviewing how translation issues are formatted and how translation changes reach the master branch. Define how added languages would be detected, how existing checklist items would be updated, and when an issue should close. Done means the process handles already translated languages and removes the need for manual checklist updates.