Beasts don’t speak any language in DnD 5e, with a few specific exceptions. For example, Giant Eagles speak Giant Eagle, and Giant Elk speak Giant Elk.

Many of these more intelligent beasts can also understand languages, like Giant Eagles understand Common and Auran, while Giant Elk understand Common, Elvish, and Sylvan. However, beasts cannot speak these languages.

Forest Gnomes have the ability to speak with small beasts through sounds and gestures, but this is not a language.

Likewise, the spell Speak with Animals lets you verbally communicate with beast, but this is a function of the spell rather than tapping into a specific beast language.