I don't "speak" any second language well enough to live a normal life in the country (except Esperanto, which has no country). But using my own geometric scale, in which 1.0 means you know one word and each higher point multiplies your vocabulary by 3.2 (assuming comparable advances in grammar and pronunciation), I am
8.5 in English
7.5 in Esperanto
7.0 in Spanish
6.5 in German
6.0 in Mandarin
5.5 in Portuguese
5.5 in Italian
5.0 in French
5.0 in Catalan
4.5 in pan-Slavonic (the basic vocabulary is almost identical with different phonetics in Russian, Czech, Bulgarian, Serbo-Croatian, etc.)
4.0 in pan-Scandinavian (same goes for Danish, Swedish, Norwegian, and Icelandic, as someone already pointed out)
I do much better in reading and writing, because I can just sit here with a dictionary.