I love this addition to the game, however I have these concerns...
Very few mobs of their races actually speak in their native language at all. In fact, some races don't even speak at all. (Not because they can't, they just don't.) Leaving only PCs able to teach some languages.
Illithids still use a "pretend" language before this was implemented. Let's change them to utilize their proper language.
There is supposed to be some mob that wanders around, letting others practice languages? I've been back for awhile. Never once have I seen it and half the time I'm actively looking for the dang mob. Can we put some mobs in a damnable library that can teach?
there are mobs that teach, they just spawn randomly across the world from what i have seen. another thing about the language for me is that if you have a char that was around before implementation then he doesnt even know common, I have a illithid with such problems. I don't know if there is a way to fix this but I just never tried
Each normal language (some can only be learned through special means, afaik) can be taught by a racial mob in the area most associated with that race. They stay put.
There is also the Laconic Linguist, who teleports between every area in the game randomly. He teaches all the languages that aren't super-secret.
When I type learn I see what look to be "practices." For languages.
How do I utilize them? Can it only be done with this Linguist? What if I already have a couple % of a language? They don't seem to get better with practice of using either.
There is a little trick to getting the linguist to help you out, if you're lucky enough to find him.
As Naru mentioned most races have a single teacher somewhere, look around.
There are languages like demonic, divine, archaic and others that are very very rare, and have no 'teacher'. For those you will likely only get them from an imm.