I just started reading the fall of reach book and here's a line that proves translators existed at some point in the Halo universe (unless that book's non-canon now)
Taken from the first page of the prologue: (talking about grunts) "They reminded Chief of biped dogs, not only in appearance, but because their speech- even with the new translation software- was an odd combination of high-pitched squeaks, guttural barks, and growls"
This was from the battle of Jericho Vll, which was 17 years before Master Chief was in a game, so maybe things could have happened over the years to the translation software, or maybe it was new armor. I don't know, but I found this thread interesting after I just read something about translation software earlier today.