If you want to know the "deep history" of the world, Draconic and Giant are necessary, and if you want to get a sense of the world's place in the multiverse, Celestial, Abyssal, Primordial and Infernal are literally key to some archaeology. Undercommon works the same, but for the Underdark. All these sorts of languages in my game can be picked up pretty readily in any cosmopolitan environment. Goblinoids and Orcs and the like have a mix of people integrated with Common speakers but like Elves and Dwarves have ancestral enclaves or groups who prefer to speak their own language. Gnomes find non Gnomes making an effort amusing. Halflings have always spoken common as far as they remember. Elves and Dwarves appreciate the use of their languages in their ancestral enclaves, but most of their populations have integrated with the common speaking culture. In my world, Common gets you by on most of the "Mainland." There's some enclaves from other places that have a different sort of common, but members of those enclaves interacting with the games "known world" tend to know common. Undercommon is the common of the Underdark. Celestial is the language of angels and beings in the league, so to speak.
![ravenloft languages ravenloft languages](https://neverwintervault.org/sites/neverwintervault.org/files/project/6032/images/1266458760fullres.jpg)
Elvish could be a "good" language, but if you want like the forresty forces of good, you might want Sylvan too. That said, it depends on your DM's game world. So language, somewhat like alignment, only really matters if the DM wants to make it or a thing or players prompt to make it a thing (for example, if I had in my game a character who really put resources into making a character as something of a linguists, they're going to have places to shine).