I did think of another solution, which is making it so that the minimum topic title length could be set per category, if there are multiple categories with different languages.
For core, it would probably still depend on how frequently used it would be – but it could also be done in a plugin.
The spam reason / clarity of titles is mainly why it is in the hands of the admins rather than users. Though I also get how frustrating it would be as a user in a multi-language forum at present.