For FIRST robotics in particular, Java and LabView are the most commonly used languages because they are the two for which a robust library is maintained by Worcester Polytechnic Institute for use in the competition.
But I have long been of the opinion that both languages are kind of an ill fit for the application. Python is making some headway and I think it might be a better fit; It has some advantages on legibility, it has an optional static typing system, and it does support coroutines.
Thankfully, very few teams are still using LabView at this point and WPILib primarily targets C++ and Java, with first-party Python support coming next season.
But I have long been of the opinion that both languages are kind of an ill fit for the application. Python is making some headway and I think it might be a better fit; It has some advantages on legibility, it has an optional static typing system, and it does support coroutines.