Now that Mask of the Betrayer has been released in Europe, it's been discovered that installation can be problematic for some. Rob McGinnis has posted some tips for installation as well as links to multi-language hot fix files:

When installing MoTB, please use the following instructions:

1. Install NWN2
2. Patch NWN2 to the latest version (1.10 as of Sept. 29, 2007)
3. Install Mask of The Betrayer
4. Download and apply the hot fix for your language, listed below.

Italian
French
German
English
Spanish

If you do not apply the hot fixes, when you attempt to play the game you will see sections of missing text and the Campaign name will say it is undefined.