At some point in the early 20th century, sci-fi started taking place in the future more often than not.
From there to people thinking sci-fi is about the future was just one step.
So it happens that in the silver age of sci-fi, characters had names seemingly made from a random jumble of syllables. Note however that they still always had a first name and surname, in this order, and very pronounceable in English.
The Star Trek TNG episode Ensign Ro shouldn't have been so remarkable simply for bringing up this very real cultural issue, but there you have it. The now-famous text Falsehoods Programmers Believe About Names wouldn't exist for another two decades.
It's the same with other things we used to get in sci-fi back then: bizarre fashions. Bizarre dances. What was the point? One of the things that made Star Wars remarkable was the use of real-world architecture from African countries that most people, myself included, would never have seen otherwise. Much better than everyone filming at that one university from Canada. You know which.
Funny how real cultures that exist right here on Earth often seem alien to us.
That's just it, you see: sci-fi isn't about distant worlds from the distant future, or by the same token for audiences from those distant future worlds.
Never mind that most writers (linguists excepted) likely can't begin to guess what languages we'll speak thousands of years from now. In any event, they'll resemble modern English, or Chinese, about as much as Italian resembles Latin. If you have the skills, by all means, make up a constructed language, calendar and so on. More power to you! Those are often fun.
Otherwise, you're better off using what TVTropes calls the Translation Convention: simply using English, French, German or what have you as stand-ins for the different languages people speak out there in their era. It's not fool-proof: I tumbled all the way into Unfortunate Implications territory once, and made a friend very sad. But for the most part, it helps me get the point across.
No, it's not Space Christianity, it's whatever equivalent might exist by the time icons of the Virgin Mary will be as mysterious to historians as frescoes of Minoan bull games are nowadays.
No, it's not Fantasy Ukraine. I couldn't even imagine the ongoing crisis three years and a half ago. But such is the curse of the writer.
Some readers don't like it. Guess it's too on-the-nose sometimes. And maybe I should be more daring. Embrace escapism.
It's a deal then. But in the mean time, the Translation Convention is a handy tool. It offers good starting points, if nothing else. Keeps me grounded, too.
Dreams are nice. Remembering them when you wake up is even better.