For Chinese the words that are in both lists have the same numeric ID.  If I understand it correctly they contain exactly the same words, it's just that they use different variants of Chinese symbols (simplified vs. traditional).   This may be bad, because the traditional Chinese seed produces different keys than the simplified Chinese seed, even though they both match the checksum.

For French vs. English, the situation is not so bad.  You have some seeds where you can't say whether they are French or English, sometimes the checksum is okay for French, sometimes for English and sometimes for both languages.  But the keys produced are at least the same (unless the French and English seeds differ by accents).  The 128/256 bit seed from which the passphrases were produced is not used for anything, so it is not so bad if they differ.

Changing the word lists opens new problems.  We can't know how many French/Spanish/Chinese/Japanese seeds are already in use.  I think, the most practical solution is to just drop the requirement that the word lists are sorted and require a linear search.  When the language is not unique, check all supported languages and accept the seed if it has the right checksum for at least one language.  Auto correction requires that the user chooses the language before entering the seed. In the end the private keys are computed from the seed, ignoring the language for which it was computed. The checksum is only there to prevent people from doing stupid things like inventing their own seed with low entropy.