Any time a checksum is invalid, warn the user the phrase just isn't something created by your app, and ask whenever they wish to use it in any case. This fashion, your application only has to keep the wordlists in your supported languages, however, you can recover phrases created by https://isocialfans.com/story4264998/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting