Three mother tongues:
Limburgic
Dutch
German
Learned later:
English, fairly fluent
Esperanto, fairly fluent
French, not yet fluent but enough to get around well
Russian, halting enough for basic conversation and debating with policemen
Lithuanian, forgotten most of it
Only passive knowledge:
Letzeburgisch
Afrikaans
a wide array of German dialects
Some bits and pieces of other European languages
I've published in Dutch, German, English and Esperanto.