Ref: https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki
You can generate mnemonic from 12 / 15 / 18 / 21 / 24 words, from several languages listed here https://github.com/bitcoin/bips/blob/master/bip-0039/bip-0039-wordlists.md
