I take some issue with the implied suggestion that Brainfuck isn't serious, but that's probably my arts degree talking.

Anyway, under the assumption that I'm correctly guessing what you have in mind when using the words "serious language", Uiua certainly qualifies. The author is very passionate about exploring and discovering "the good parts" of the design space of the array language paradigm, and has put a ton of work into making it accessible and practically useful within the constraints of being an interpreted language that autoformats its source code to at-first exotic looking maths symbols.