"- Speak and understand all learnable Languages for 1 turn per warlock level."
This is a cool idea, but feels a little lackluster for something that expends a precious feat. You can speak and understand what's said aloud, but that intricate, powerful, unholy understanding doesn't apply to reading what you're speaking.
Motion to allow, at least, that as you can understand all learnable languages, you can also read all learnable languages for the duration of the spell.