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.