It is "gente strana" because adjectives generally follow the noun. Additionally there are some common adjectives like caro and bello that come before the noun. Check this link to see which ones come before the noun. http://italian.about.com/library/weekly/aa072199b.htm
EDIT: I was probably tired when I misread the question :) it is "strana" because "la gente" is singular noun in Italian even though it translates to "the people" (plural)
Unfortunately official translations are sometimes invisible (they said it is a bug and they are working on it.)
Your answer is also the main translation.
I don't think it can be translated as strangers = unknown people = sconosciuti = stranieri
gente strana = strange/odd people means "people that are acting or looking strange".