I've recently noticed a similarity between these 2 phenomena:
- the joy of listing the number of languages which we have worked
- the allure of listing the number of major cities to which we have traveled
Most people will qualify their travel list, by saying, "well I've been through London, but just the airport so that doesn't really count". (Indeed, it doesn't.)
I think geeks are less likely to qualify their language list: at least I don't. You won't catch me saying "well I've written Hello, World in Haskell so that doesn't really count".
Now to be honest, I wouldn't even put Haskell on the list, but it is true that a static list of my languages doesn't give anyone a real sense of my experience.
Staying at the Language Resort
A better example, for me, is Python. I have been proselytizing Python for a long time: the spirit of the language appeals to me and I am never happier than when working with the language.
But to be honest, I stay at "Club Python": a sunny resort where the beaches are pristine and the drinks are free. Life is easy.
I've never had to deal with packaging a Python app; I've never had to internationalize one. Or even really debug his/her lousy code in a commercial Python app. I certainly haven't had to deal with scaling issues.
Not to say that this can't be done in Python: I just haven't done it.
Lonely Planet for Languages
To mix metaphors, be sure to evaluate the experience of evangelists. Don't take travel advice from someone who went through the airport. If you are looking for a resort, that's fine, but what we really want is someone who knows where the locals eat and where the food is fresh. A battle-scarred veteran who has suffered an exotic fever and has seen all 4 seasons in the locale. One who has the guts to try speaking the local dialect, and yet the cunning to escape a pub alive when they have inadvertently insulted the national soccer/football team.
For a given language, seek those who could write a Lonely Planet guide for the language.