Language related spells have always been really weird to me, in 5e. Like, how do they work? Do they draw from the collective memory? Is there a record of all languages? What about slangs and regional dialects? What if I'm speaking a conlang that only my sister and I know?
Narratively, they remove all tension when interacting with a foreign culture. At higher levels, they also make language proficiencies useless.
Not to mention how the world would change if there are no linguistic barriers.