Lookup Companion for Wikipedia 2.0 is released! In this update we have fixed the "Open In Tab" bug. Also users are now free to use Wikipedia in any available languages.
To use a custom language, please go to options page and select "Custom", and enter the language code (a two-letter code) of the language you would like to use.
Click "OK" and "Save" to confirm your changes. That's it!
For the list of available languages, please check out this list.