In old times native Americans hunted in whistles, calls ,and sign. I imagine that sasquatch has managed to master something similar over time. It only stands to reason that they have evolved to their habitat. They probably have specific dialects as well.
I would imagine, given enough of this “language” to study, and the context, you could figure it out just like you can with other languages. The problem would be the lack of enough recorded sasquatch language/whistles with context. Haha, I’m good at languages, but I have never been able to whistle to save my life. I would plum be outta luck! (I’m laughing imagining a sasquatch with it’s head cocked to the side, trying to figure out what the heck I’m doing while I’m desperately trying to get a whistle out. Hahaha!)