Just take anyone who speaks a second language and ask them to explain their expertise in the second language. Almost everyone will start sounding stupid trying to do the translation in their head to the second language.
Edit: Just to be clear, I don't think said person is stupid at all. There's just difficulty speaking about a concept you would innately know and have learned in one language and translate it to a second one. Except for all those genius polyglots out there of course.
That only applies to people who don't speak that language well enough to go straight from concept to words in that language in their minds, without passing via an intermediary language.
People who need to translate between languages in their heads as they speak in a second language are at the same level in speaking foreign languages as those who need to count with their fingers are in Maths.
On the upside, once you start going directly from concept to words in a language you're reasonable good at, it becomes possible to do it in languages you're not at all good at.
I have a bit of a different experience. As an engineer, I mostly use English at work, so I usually have issues explaining my area of expertise in my mother tongue and other languages I know. There are lots of terms I know only the English words , so I end up using the term in English or try to translate it and it sounds stupid.
Well yeah, ok, I have the same issue too because I've spent most of my career abroad and learned many technical terms in English and even Dutch, so for those things I have no idea what the words for it are in my native tongue.
But I just use whatever word I do know when I don't quite know the technical word in the language I'm speaking, and it's the same when speaking my native tongue as when speaking some foreign language which is not English: if I miss a word in that language I just almost seamlessly fit in the English word for it instead (or, in the case of German, I might use a Dutch word and hope it just sounds like the right word said in a strange way) and clarify if requested.
That's not at all the same as having tons of trouble speaking because you're translating in your mind.
As far as I can tell it doesn't sound at all stupid, though maybe that's because I'm generally using a foreign language to fill in the gaps in my knowledge of yet another foreign language.
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.
It is easy to answer that particular question. I'd just answer with: Probably somewhere at B1 or B2 level, although I haven't been assessed in ages regarding that.
Sometimes it feels like the classic you said you like croissants, that must mean you hate bagels
You put in so much effort to make your point crystal clear, choosing your words extra carefully to form a sentence that means exactly what you need it to mean, and then some people just interpret the wildest things.