The question whether Occitan is an independent language is really a political, rather than a linguistic question. For long years Ukrainian was regarded as the "Little Russian dialect of Russian," and the Soviet authorities did not permit the manufacture of typewriters with a keyboard representing the Ukrainian alphabet, which is slightly different from Russian. Yet it is now the official language of the independent Ukraine. Maltese is an Arabic dialect, but is considered a different language because it lives in the world of Christendom rather than Islam. On the other hand Mogrebi, spoken in Morocco is considered Arabic, even though it is widely divergent from standard Arabic, and is probably not a direct descendant of classical Arabic. The situations with Serbo-Croatian and Hindi-Urdu (each of which is virtually one language) are written in different scripts according to the religious community to which the speaker belongs. Czech and Slovak are considered separate languages, although they share the same script and differ rather little, because anciently the Czech lands looked toward Germany and Slovakia toward Hungary in cultural matters.
Since the Occitan speaking lands are not independent, their language is generally regarded as a French dialect, despite its long literary history going back to the troubadors.
This important source of Lingua Franca semantic material has been largely overlooked, since Occitan is largely invisible. Schuchardt, however, does indeed refer in his essay to Southern French as a source of Lingua Franca.
Occitan words may be checked in Lexic englés-occitan. Even a cursory glance will assure the reader that the language is substantially different from standard French. For more information on Occitan, enter Occitan in your favorite search engine. A useful French-Occitan printed dictionary is Roger Barthe, Lexique Français-Occitan (Paris, 1973)