Bip39 Standard. Though there are BIP39 wordlists in languages other than English, it's strongly not suggested to utilize non-English words for wallet backups. It might make restoring the wallet difficult or extremely hard. Anyone else who discovers the phrase can steal the bitcoins. It has to be saved top secret, https://social-medialink.com/story4181717/bip39-https-linktr-ee-bip39-getting-my-bip39-passphrase-to-work