The adjective dialectical describes ideas reasoned about through dialectic, or the interaction of opposing or contradictory ideas. However, it is often used to in a rather different sense: ‘pertaining to dialects’. For that sense, the more natural word—and here I am being moderately prescriptivist, or at least distinctivist—is dialectal. Dialectical used for this latter sense is, in my opinion, a solecism. This essentially preserves a nice distinction, like the ones between classic and classical and between economic and economical. And certainly there are linguists who have good reason to write about both dialects and dialectics, perhaps even in the same study.