Quantum language ( i.e., the linguistic Copenhagen interpretation of quantum mechanics) was proposed as the metaphysical and linguistic turn of the Copenhagen interpretation. This turn from physics to language does not only realize the remarkable extension of quantum mechanics but also yield 
the linguistic turn of Descartes=Kant epistemology. Also, this has a merit that the wave function collapse can be completely understood.
(See https://ishikawa.math.keio.ac.jp/indexe.html )