This is a common writing technique. 

The readers is looking from the outside in so its best to paint the picture in broad strokes so no one gets bogged down in minor details. You call a language elvish and they don't have to struggle to remember who's language it is. 

You'll do the same in some other areas of your life, maybe (if you aren't from the US) you say someone has an american accent but even if we ignore the fact that south americans are still technically americans then people in the states will talk about texan accents and new york accents. But outside the states we paint in broader strokes because the details aren't important to get our points across.

Thats my opinion at least ^^