When you encrypt your DragonFly boot drive, initrd(7) is run to get your system online and able to accept a password to decrypt the drive. So far, so good. The initrd program is a minimal userland designed to be small, and it generally works. However, it assumes a QWERTY keyboard. If you’re Pierre-Alain TORET and normally use an AZERTY (in this case French) keyboard, that makes it difficult to type the decryption phrase.
It’s possible to patch a different keyboard layout into initrd, and he has documented just how to do that.