Wendersnaven.com (a resource for nwn2 builders)

There is currently a stickied post the official forums concerning tlk files:

Current word from Obsidian programmer Erik Novales is:

Custom TLK support in the toolset will be in the next patch. In addition, specifying string refs as hex values in 2DAs will also work. This works similarly to how it did in NWN1 -- flipping the high bit on a string ref signifies usage of the module-specific TLK.

The talk tables are indeed UTF-8.