"This is a Senegalese dish."
Translation:C'est un plat sénégalais.
I don't think sénégalis is a thing, but assuming you meant sénégalais, I think that would mean something like "a plate of Senegalese" because it is in the form of an expression of quantity e.g. un plat de couscous = a plate of couscous. An adjective like sénégalais comes right after the noun.