google tells me that 3e Xvarts can be found in Dragon #339. the article says they are "small", speak Goblin and those with an Int score of 12+ also speak Draconic
Ah yes I recall seeing this article in my Dragon magazine collection. It brought a smile to my face since the only other place I saw these critters was in the BG1 CRPG. Ah, such swell creatures they are.