Love it, always thought this would be a great idea.
Ive always thought a plot heavy game would be a great way to learn Irish. As opposed to a shooter or racing game etc where there is almost no audio etc.
Something like the Elder scrolls RPG's would be good to Mod as they are full of conversations and you get to make conversation choices. You could even have different races in the game speaking different dialects.
I would certainly have done my Irish home work back in school if it involved playing a game. I would probably have only done Irish homework
