A constraint could be a language that your company says you must use - so that's the 'best' language to use. A constraint could be an inability to hire someone with experience with a language you want to use. A constraint could be a tight deadline that precludes you learning a new language that might be more useful than the language you already know. And, of course, there are always technical constraints between various pieces of software that excludes or encourages the use of a language.
So, I'm pragmatic regarding programming languages. What works works. Let's deliver something and move on the next cool thing to code.