One of the key appeals of the Minions is their nonsensical gibberish. It's sort of followable, but only kinda English - it is, put simply, rather silly. Well, not exactly - their language is actually much more developed than it may seem. A lot of what their saying through the silly voices makes sense in certain languages; it's just that it's so many different languages it's hard to tell. Their greetings and thank yous are directly lifted from around the world and "Miam Miam", which one prehistoric Minion says to describe a banana isn't a silly version of "Yum Yum", but a direct French translation of "yummy". As well as providing a variety of different linguistic jokes, this also makes sense in the movie's world; the Minions have travelled all the round the world searching for their master, so of course will have picked up various dialects.
