I believe that in both case there is a placebo effect: if you have to program in a language you don't like, you'll be unmotivated, bitch about it frequently etc

I believe that in both case there is a placebo effect: if you have to program in a language you don't like, you'll be unmotivated, bitch about it frequently etc. If you program in a language you like, it doesn't really matter how well it is fitted to the job, because you'll take shortcomings as challenges and sort of want to prove it can be done productively. "The right tool for the right job" is only part of the story. Proficiency can go along way.