Schlumpf is one of the "lost" languages of the Smurfs in the EMPATH: The Luckiest Smurf story series. It is equivalent to the human language of German, following the same language rules of grammar. At the present time of the story series, Schlumpf is hardly used by any Smurf except for Empath, who has mastered all the lost languages of the Smurfs. Culinary Smurf, though a descendant of the Schlumpf clan, hardly knows how to speak in Schlumpf.
NOTE: Schlumpf is the actual German name for Smurf.