I've been perusing Makoni & Pennycook's Disinventing and Reconstituting Languages -- some fascinating ideas, but I don't think I'll jump in wholeheartedly. Even if existence of discrete languages can be shown to be 'false' -- or at least if the beliefs that laypeople hold about what languages are can be shown to be dangerous and/or harmful, which can certainly be true -- I'd prefer to retain the concept of 'a language' just as we tend to retain concepts like 'native/nonnative speaker' or even' race'/'ethnicity'. They are terms that may be deployed in problematic ways but my tendency is to stick with 'commonsense' definitions and work on ways of understanding language that are a) nuanced, b) likely to be useful/helpful in educational and other social contexts, and c) plausibly acceptable by non-specialists. I can't see 'language isn't a thing' meeting the criteria for c).
Trevor Pateman (who I hadn't heard of until, um, today) writes in his essay "What is English if not a language?" "