They generally ask themselves if something sounds correct, and if it does count it as part of a language. Psychologists want to know about the people using the language. Example of markedness. A. Language is fundamental. B. Intellectual concerns.
Language is an interesting problem.
C. Practical concerns. The task of translating all of this stuff was enormous. The government funded a lot of research by psychologists and computer scientists to automate this task. Now, business needs for machine translation are still driving research in the area. If we work it out we can help people who have strokes or particular language deficits to recover.