Assuming you're talking about desktop applications and, in that case, you can use almost any language (provided it has bindings to graphic libraries/interfaces).
So, I'll mention what I would use:
Python: The nice thing about python is that it has libraries for almost anything. One of the few things one can't do with python is front-end web development and, even then, there are transpilers to js and web-assembly is around the corner. But I digress; anyway PyQT is one of the best choices, or so I've seen, as far as graphic libraries come.
Javascript: For all the talk about it supposedly being a limited language, one needs to see no further than Gnome Shell to see what can be done with js in the desktop.
C/C++: They are the no-brainer choice. Examples of what can be done with them: Most web browsers, most office suites, most media players, most media editors, most file browsers, most everything really.