Bip39 Standard. Despite the fact that there are BIP39 wordlists in languages besides English, it is actually strongly not proposed to employ non-English words for wallet backups. It'd make restoring the wallet difficult or extremely hard. BIP39 specifies a list of 2048 words from which the mnemonic phrase is decided https://tealbookmarks.com/story18730883/ian-coleman-bip39-https-linktr-ee-bip39-the-basic-principles-of-bip39-mnemonic