ContentTranslation exists since 2014 (according to https://www.mediawiki.org/wiki/Content_translation) or even since Oct 2013 (according to git log --reverse in mediawiki/extensions/ContentTranslation repo) with more than 6 years of development, tests, inputs from users and beta testing, I don't see a reason to keep it as a Beta feature anymore.

Keeping it as beta feature prevent from new comers to easily use it.

I suggest to make a technical decision whether or not ContentTranslation from technical perspective is ready to be out of Beta by default.
If there are issues that are still prevent it from getting out of beta in specific language, we can opt-out them and keep them in Beta, while creating tasks to define the gaps required to get it mature in those languages.

Related tasks: T235175 to document the beta success of failure