Humans were living there. Elves arrived. The Elves taught the humans many things including a simplified version of their own language, now known as “Common.”If human characters speak an additional language, it will probably be dialect of Common that’s spoken in their home area.
Pure elvish is the language of educated people, though most humans know a few words.Not all humans were so eager to welcome the elves and those who have continued to live aprt in the swamps, forests, and mountains, are known as Gray People. They speak their own language, which includes many local variants. As with elvish, everyone knows a few words. Grayspeak is great for swearing.
The Hobbits’ language sounds like a dialect of common, though like other common dialects, its accent can be exaggerated to become nearly unintelligible to outsiders. All hobbits understand each other when they speak this language, even if they come from areas very far apart form one another.There’s little reason to know dwarfish or gnomish as most trade is conducted with members of these groups who speak perfect common. Dwarvish is a very difficult language both to speak and to read/write.
Only people with very specialized knowledge will have made a point of learning Oanoise, the language of a group of settlers/invaders/guests who were driven out of Alyan a century ago. Even those who “know” Oanoise might be able to do little more to recognize certain characters. Pronunciation varies from one sage to another.
Orcish, goblin, hobgoblin, etc. The monster languages are almost unknown. Some sages argue that these creatures do not exist and that their languages have been artificially created by hoaxsters.