Usually I give thanks, or I might ask if there's anything more I can do to increase my connectedness with them / the land around me. As for a specific language, in animist spiritualities, a lot of references are made to the 'hidden' language. I know it as Nembhut. But my experiences are that most land spirits transcend our capricious human languages, and still make their wants/needs known if people listen.
A tree spirit is a tree, in its every day life. A mountain spirit is a mountain. Most land spirits occupy the land, just as we occupy our homes or our workplaces. But, I'm only human, who knows what many spirits do in their every day life. Land spirits though - based on their name - are connected and stay connected to the land.