That's why they should just mention it and move on, instead of doing weird, immersion disrupting things like having people lips move while other words come out or doing anything to mention it again. If it falls apart when you think about it, but you have to do it for the show to work dramatically, just make it so people don't think about it much. Don't bring it up. Don't do things (like idiom jokes) that make you think about it.
transporter is even worse, can't even remember that many translator shenanigan episodes.
however, while they might be simple plot devices they are (usually) used in a way it works and the only people that think too much about it are nerds like us.
which reminds me, galaxy quest was running at a friends place recently, always forget how fucking good it is.
what is this timeline where a parody is better trek than the official shit?
What makes no sense at all is why R2 talks in beeps and squeaks that only C3PO can understand. What language does R2 speak anyway? If it's meant to be a kind of machine code, why does it take so long for him to say short sentences? They built a sentient artificial intelligence with less ability to articulate words than a child's Speak and Spell toy circa 1979? Why?
Droids in general don't make much sense in Star Wars. Why does an X-wing need a robot copilot? What exactly is the point of a protocol droid and why would you want that capability rendered in 6ft tall mincing gold robot form instead of a tablet you can easily carry in your pocket? Maybe George Lucas didn't know what software was.
Star Trek goes too far in the opposite direction, apart from Data the writers don't seem to like robots very much even though you might expect the USS Enterprise to use drones for a lot of different jobs.
star wars is science fantasy, how technology works was never really the focus (just look at the technological progression which makes zero sense). that's why r2 makes funny noises so c3po can answer "no,
you are a faggot" as some kind of dialog.
however c3po makes sense, he's basically a walking interpreter, and the protocol part imply that he also knows about customs and shit, so you'd want to bring him along just for that. "on this planet you great each other by holding up a fist and raise your middle finger". also elegantly solves the problem of not having to speak into some device you have to carry around, then shove it in someone's face to repeat it in their language.
as for starfleet and droids, my assumption is that they never really put much work in that field. noonien song was always depicted as some weird eccentric, and starfleet had more than enough manpower for most stuff, which also brought a versatility no drone could ever fill, so trying to cram AI into a human-sized body wasn't that interesting (another aspect st: patrick fucked up).
for industrial stuff they probably had more than enough automation with advanced AI, but that was hardly ever shown. only one I really remember was the part where the EMH was mining dilithium (which was more about the drama anyway, you can't tell me someone advanced as starfleet has to collect that shit
by hand)