Bip39. Whilst there are actually BIP39 wordlists in languages in addition to English, it is actually strongly not proposed to use non-English words for wallet backups. It might make restoring the wallet difficult or impossible. BIP39 specifies a list of 2048 words from which the mnemonic phrase is decided on. https://bookmarkingdelta.com/story19536833/bip39-wallets-https-linktr-ee-bip39-the-bip39-wallet-diaries