MTL stands for Machine Translation, basically the game's translated using a machine.
I read it up somewhere in this site someone said because it's the easiest way to translate a game.
Most cases after the MTL it would be a mess or sometimes even ruin the code of the game (I don't know the detail about that since I've never translate a game before) so after the MTL some translators would edit the text once again (usually called edited MTL).
The problem I see lots of people have with MTL is when you can't understand what's going on at all especially when it comes to game that requires you to read, understand, and choose your choice.
So people often refers to playing MTL game as something like "poet time" since the translated texts are sometimes very random and TBH for me it changes the tone of the game to comedy, have you ever laugh while you masturbate?