Welter wrote almost exclusively in the
German language. His drama
Griselinde (1901) served the Luxembourg composer Alfred Kowalsky as
libretto for his opera of the same name. Around the turn of the century, Welter's interest was in themes from Luxembourgish mythology and history, but also especially literature in the French minority language "langue d'oc" (Provencal), which had been reinvigorated by the Félibrige school. He corresponded with famous German Romanist as Eduard Koschwitz and August Bertuch and traveled twice to
Maillane ( Bouches-du-Rhône) to
Frédéric Mistral (Mistral Frederi), the "chef de file" of this movement. As one of the German Romanists, he was not indifferent to the efforts that the award of the 1904
Nobel Prize in Literature led to Mistral. In reported Welter in his travelogue "Hohesonne days. A holiday book from Provence and Tunisia "(1912). ==Honours==