When a checksum is invalid, warn the user which the phrase is not really one thing produced by your app, and talk to should they would want to use it in any case. This way, your application only really should keep the wordlists for your supported languages, but you can https://checkbookmarks.com/story4359492/how-much-you-need-to-expect-you-ll-pay-for-a-good-valid-bip39-seed-phrase