What I find more strange them seeming to speak English, is that it's 20th century English.
Why? Surely the setting in our
UTs should be 20th (or, nowadays, 21st) century English, even if the setting in Picard's UT is for 24th century English output and possibly 17th century French input.
That is, it's unlikely that any of the language we hear is untranslated. Most often it's probably twice translated - first for the benefit of the heroes, then for the benefit of the audience. Sometimes the heroes don't use translators (say, VOY "Basics") but the audience still does...
Indeed, I have a hard time believing in the concept of "language" in the 24th century setting any more. What possible motivation would Picard, Worf or even Riker have for learning English when they can simply decide to speak Picardian, Worfian, and Rikerian, respectively?
Another problem I have is with the explicit limitations in the application of the UT. Why not translate things like whale speech in ST4? Why doesn't Data ask
Spot what sort of food he/she really likes? Can't Crusher tell
the microbes to piss off and leave poor O'Brien's brain alone?