What is "syldavian"

Syldavian is a fictional West Germanic language created by Hergé as the national language of Syldavia, a small fictional Balkan kingdom that serves as a major setting in many of The Adventures of Tintin stories. Hergé modeled the language on Marols, a dialect of Dutch spoken in and around Brussels. The entire corpus of the language has been analyzed by Mark Rosenfelder.