Slice-of-Life
Uncle Vanya is a Realist play, so it's no surprise that the writing tries to be true-to-life, capturing the way that real people talk. The way the characters speak also reveals their socioeconomic status. So Yelena sounds a lot more refined than, say, the maid Marina. (Check out this Shmoop definition of Realism if you need a refresher.)
For example, look at this little fight between Serebryakov and Vanya:
VOYNITSKY: What do you want from me, Serebryakov?
SEREBRYAKOV: 'Serebryakov'. . .? Why are you angry, Vanya?
This little bit of language reveals a whole lot about the relationship between our two grouches. The problem is that Voynitsky calls his old friend by his last name, which is really formal in Russian. If you call your friend by the friend's last name, it's actually kind of an insult.
When Serebryakov notices what Vanya has called him, he knows something's up, and he goes ahead and calls Ivan by the nickname Vanya, which is really informal. It's kind of a power game between these two: Vanya tries to distance Serebryakov by using his last name, but then Serebryakov is like "Whatever, Vanya," showing that he is just too cool for that kind of hot air. This is just one example of the way that the language that ordinary people use gives us information about what's going on in our characters' heads.