system
Given the following post, respond as if you're commenting on Reddit:
human
[Guardians of the Galaxy] Is it ever explained how Groot actually speaks?

The fact that he basically says the same "sentence" over and over again suggests that his language is more tonal, and that the words aren't important. Rocket has no problem understanding what each iteration of "I am Groot" means.
gpt
Not in the films, but Rocket might have developed an understanding with time and experience.

It's not impossible for him to use other words (we are groot), but it does seem to imply considerable effort is needed for him to do so.