To add to this - concur with the general sentiment of ‘use it where it adds to the fun’.
One thing I have had fun with is that long-lived creatures - elves, dragons, planar entities, gods - are going to act as stabilizing influences on language - there is still an elf here that speaks as he did 1000 years ago. This means that these stable languages are good go-to’s for trying to find common ground with strangers. Some specific cases where I have played with language recently in game:
- Players ran into some extra-planar kobolds, managed to work out they shared old draconic as a root and got into a nouns and verbs pidgin for general communication, then occasionally cast spells where it became important
- Summoning a bunch of celestial creatures to act as special effects for a bards show and getting to listen to them all chattering to each other since one of the party could speak celestial
I think having ‘there are other languages, you don’t speak all of them’ as part of the setting is good for making it seem real and lived in. For most mundane people and encounters, since most travel is slow, you will be able to figure out a pidgin or share trade common or the like - but it then helps to emphasize how far a party has traveled when they take a long voyage or cross the planes (or summon something) and then are faced with a language barrier. Make ‘figure out how to speak with people’ one of the things to sort out on a long journey but no need to make the solution very arduous.