Quote from: NotATether on September 20, 2020, 12:08:45 PM

This is not correct. As someone who's busy developing a BIP39 checker, this is only a recommended guideline. It is not strictly required to make every word have 4 unique leading letters, but it's highly discouraged not to because the more characters you need to iterate in a word to tell it apart from other words, the more likely someone's going to type the wrong word in their seed phrase.

It is definitely possible to create and use a wordlist that breaks this rule, but such a wordlist has no chance of getting merged into the BIP39's official github repository.

I'm aware. BIP39 requires the wordlist to check validity of a mnemonic phrase, which is one of many reasons why some people dislike BIP39. This can be viewed as a self-inconsistency of BIP39 spec, however I just think the fact that "wordlist flexibility" of BIP39 doesn't really work is not very important. Official English wordlist can work well, that's enough. In my opinion, the attempts to takeover BIP39 will only make the situation even worse, that the user (even machine) can't tell exact type of those 12 words at hand.