I'm not a programmer, but primary and secondary sound ok to me. I'd go with that.

I'm a Java/Kotlin programmer but I'v not heard primary and scondary prorgramming languages yet. Of course it's not wrong but it's not common. Instaed you can say something like this: I'm a Java and Swift programmer.

When you are a real programmer a language is just a nuance. You can probably say that you prefer to work in ... language, but you would not state that, for example, "Python" is your primary language. You would say: "I prefer to do ...... using ....... language". But the choice of a language would depend mostly on the job you need to do. Programming languages are not like human languages.

How about simply 'Salaries by business group'?