If I forget a word it often blanks in both languages, but increasingly I realise I can explain my job better when speaking German than English.
All my professional life has been in English. In a previous job I would get asked to review technical translations into Spanish and I struggled to do a good job, as I had no feel for what the technical Spanish was as I had never used it.
Fluency in an adopted language is an interesting thing. I learnt both Galician and Spanish growing up, but Spanish was only used at school or heard on TV, no one around me spoke it in every day life. As a consequence, if I speak Spanish what ends up happening is that I mostly speak Galician with Spanish words, if that makes sense. I think that's the case for most people starting to use the adopted language, and it takes a long time to move beyond that. I've been trying for 25 years with English, and it is really hard work.