Xanalress
To speak Xanalress in game, type -xa in Mith's Virtual Console.
Xanalress is the language of the drow. Xanalress is closely related to the language of the surface elves, but the language of Drow is the Elven from millenia ago, from when Drow and Elves were separated. Therefore it has changed from Elven as the surface Elves know it. However, the languages are still surprisingly much alike: in reality Drow and Elves speak the same language, though the dialects are different due to long separation. Xanalress is what Drow consider the High Tongue. It is blessed and pure in their eyes. That view is held because of the Drow consideration that they are above all others.
Compare the difference between Xanalress and Elven to Americans and Englishmen in the real world: Americans left Great Britain about 400 years ago. There was not much communication between the two countries with the Atlantic Ocean between them, therefore the languages went their own way, resulting in the differences between American and English as we know it. If an American goes to London, he can still understand British English, but they have words and phrases that do not match with what he has learned and vice versa. For Drow and Elves this is the same, but with much more differences, since the American-British separation is only from 400 years, while the Xanalress-Elven seperation goes back thousands of years. Each however would still understand the basic meaning of the sentence the other is speaking. Note that this is not exactly the same as the Italian-Latin seperation used as an example in Draconic: Italians can not automatically read Latin, nor could a Roman understand much of what an Italian is saying. Elves and Drow understand eachother quite well.
Note: Also see Common Drow words.