Based on her knowledge rolls, Tessa does not know if the Vegepygmies have a language, or even the ability to speak.
Dark Creepers, dark folk in general, have their own language. Those dark folk who work with others, typically also learn Undercommon, as that is the dominant language of the Underdark. Should have put that in the knowledge spoiler, I will amend it.
Certain assumptions on language could be drawn, from the combined knowledge and/or from the scene before Tessa.
If anyone intends to make a hostile act (one that would require the rolling of initiative), let me know, or just roll it, or preferably both. Would Rothgar (or anyone) wait for Tessa's evaluation before attacking an apparent threat? Or apparent slight to the honor of your comrades?