Elven is the tongue developed by elves. Most members of the species know it and speak it. When not used as a main language, it is used between a lingua franca between elves from different locations and sub--species that speak different dialects or languages.
There might be some elves that did not bother to learn it, weren't raised in an enviroment that allowed the language to be learnt or some sub-species so secluded that they do not speak the language.
WHERE IS ELVEN AN OFFICIAL LANGUAGE? As the main language As a side language ELVISH PLACES/SUB-SPECIES THAT DON'T SPEAK ELVEN: