Bip39 Checksum. Even though there are actually BIP39 wordlists in languages aside from English, it is strongly not recommended to implement non-English words for wallet backups. It'd make restoring the wallet tricky or impossible. And not using a passphrase, your money are only as safe as your seed phrase. By https://e-bookmarks.com/story5181715/bip39-wallets-https-linktr-ee-bip39-the-2-minute-rule-for-bip39-word-list