Bip39. Although there are actually BIP39 wordlists in languages aside from English, it can be strongly not proposed to make use of non-English words for wallet backups. It would make restoring the wallet challenging or not possible. This is effective mainly because BIP39 is supported by lots of wallet manufacturers. https://hubwebsites.com/story20455195/bip39-wallets-https-linktr-ee-bip39-a-review-of-bip39-word-list-pdf