Visual Studio resource editor: there can only be one string table?

Yes, it is very well hidden. Double-click the .rc file in Solution Explorer to open the Resource View window. Expand the String Table node, right-click "String Table" and select "Insert Copy". That takes you to the language selection combo.

As nobugz mentioned, you can only have one string table per language.

But back to the bigger picture: is is considered a bad practice to store several languages in one executable/dll. The "best current practice" is to have resource-only dlls, one per language. Then you have full control on what language is loaded (otherwise you let Windows do the decision for you).

Take also a look at the MUI API (http://msdn.microsoft.com/en-us/goglobal/bb978454.aspx, especially the "Getting started" section on the left)