Salaries are always measured by year afaik. You only deal with shorter timeframes when you’re working by wage or contract.
I apologize if this was already mentioned, but I believe that in the ideal computer science career track, coding is only the first phase. By your 30s/40s, you’d ideally be in some sort of management or software engineering role where you’re doing more big picture stuff and not actually typing out code.
This is why @AdminDev’s advice is good. What language you learn initially is largely inconsequential to your net earnings compared to your ability to network, earn the respect of your coworkers and stay focused.
All that said, maybe I’m missing the point and the question is only about short term earnings, in which case there are several resources online breaking down the difference in salary between different programmer positions.