I didn't test it out by using the Latin word itself in my answer, but isn't garum simply "garum" in English too. After all, there is -- by all accounts -- nothing quite like it in the modern world (except possibly in Vietnam)! We wouldn't attempt to "translate", say, spaghetti or sashimi -- so why go, here, for the pale approximation of "fish sauce"?
In another exercise I translated "garum" by "fish sauce" and Duo corrected me saying "SALTY fish sauce" so here I wrote "salty fish sauce" and I was flagged wrong because the correct answer was "FISH SAUCE" so GODDMKLMEFJPMFHFIHCV DUO ! MAKE A CHOICE eiomtferjhptnhsr* !!!!