Humanity grew up with hundreds of languages in use on the same planet. Most other worlds (both in UF and generally throughout sci-fi) seem to be monolingual, or at least far less diverse in language terms.

Given that, we may have been the only ones who found a compelling need for "international" signage.

And when others needed it (if only for the stupid human tourists exploding out into the Galaxy after First Contact), it was easier to borrow ours instead of creating new.