Sindassi

Sindassi was the term used for the blood elves' language in an early alpha build of World of Warcraft: The Burning Crusade, but is no longer used in the current version. In the current version they speak Thalassian. Sindassi is likely not part of lore.

Sindassi was to be a new language created by the blood elves to separate themselves from their past, and to help prevent the Alliance (which still includes their high elven and half-elven cousins) from learning their secrets. Even though the blood elves were established less than ten years before World of Warcraft, it is not identical to the far older high elven language, Thalassian. Both Sindassi and Thalassian are derivatives of the ancient dialect of the night elves (now known as Darnassian). However, most blood elves continue to speak Thalassian.

Origin of the name
The word Sindassi may well be a reference to the word, the language of the Elves of Beleriand in J. R. R. Tolkien's The Silmarillion. The Sindassi/Sindarin connection is underlined by the fact that some of the Blood Elves' aesthetic tastes (pale reds and golds, autumn trees, etc., not the green crystals) parallel those of the Sindar from the Lord of the Rings film trilogy.