They can’t speak English though. In fact the scene this screenshot is from is them trapped in the past unable to communicate because their universal translators are offline. I would assume Quark speaks Federation Standard, but apparently that’s not close enough to English to figure out what they’re saying in the 40s
One thing I’ve always wondered, and this is hardly the most unbelievable aspect of the science fiction elements of this show but it’s one of the most pervasive and constant; why don’t we ever hear the native languages of the aliens underneath the sounds of the universal translators? Most, although not all, of them speak by vibrating the air, so where are those sounds disappearing to?
This was a plotpoint in DS9 where the UT didn’t picked up the nuances of a language but the mutants who were able to comprehend the language deciphered what was really meant.