In my country in Catalonia, usually all people speak two languages Catalan and Spanish. I'm lucky because I can speak and think in Catalan but in Spanish too. I don't need mental translation for change from Catalan to Spanish or Spanish to Catalan.
I grew up speaking Spanish only because my grandmother only spoke Spanish, and when I was a kid in my home usually we only spoke Spanish. I learned Catalan hearing my parents speak Catalan.
After, I learned Catalan at "Centre de Normalitazació Lingüística" in Tarragona, and now I love speak and write Catalan, and I love speak and write Spanish.
I think my two languages are beatiful. I hope some day I'll can say the same about the English language.