I concur, though most of the traits you mention are not problem-specific. When putting a language into "your toolbox" you indeed SHOULD focus on "popularity, m

I concur, though most of the traits you mention are not problem-specific. When putting a language into "your toolbox" you indeed SHOULD focus on "popularity, maintainability, being able to hire." However, when picking which of the languages you have learnt to apply to a given problem you need to know their relative strengths. Most of the strengths you mention help you pick the "best in class" language. But only the problem can tell you which subset of langauges you are picking from. Sometimes the best possible tool for your problem is going to be unpopular.