That depends on how you learn the second language. I speak three languages, but I learned them organically. If I speak in English, then I also think in English at that time. But that leads to a different problem - I cannot translate between languages I know. I can explain what is written in language A to a person speaking language B, but that won't be a translation, it will be just a free form description. My brain just don't have connections between words in different languages. I understand them, but can't make links between them.