We've seen more than a few MCU characters visit Earth (or people from Earth talking with MCU characters off-Earth), but no one has (to my memory) had language issues.
When Thor first visits Earth, he has no problems in communication (culture shock, yes, but not communication). Carol Danvers in Captain Marvel makes a passing mention of a "Universal Translator", but I feel that this is humour rather than fact-based since I don't recall any other character make mention of this.
I don't believe that Tony Stark has invented a translation device because he may have mentioned it a few times.
Is the language issue explained, or is it simply ignored?