Based on maven-gettext-plugin version 1.2.3:

I've a webapp that uses Freemarker templates. The one webapp uses a different 
template directory for each type of build. To make this usable for our team, we 
moved the template directories outside the project. As the maven-gettext-plugin 
uses only paths relative to the given sourceDirectory, it won't work for my 
situation.

I've created a patch to make the maven-gettext-plugin use absolute paths for 
the source files and the extraSourceFiles, each dependend on it's 
sourceDirectory and extraSourceFiles.directory (respectively).

Hopefully this can be implemented in the next release.

Kind regards,
Patrick van Dissel