Yes, that is the official answer. In LG, the Drow language is
Undercommon.
AFAIK, there are two variations of Flan that are actually distinct:
Flan and Ur-Flan Temple Dialect. Flan encompasses Ancient Flan and Ur-
Flan Temple Dialect is a rather distinct way of writing, used to keep
secrets by the Ur-Flan priests.
Britt Frey
Living Greyhawk Circle - IUZ Metaregion