I think you can’t accept that there are many concepts that
can’t be expressed in any language other than English.
I cannot accept such an absurdity, because it is false. I am also a scientist trained in theoretical physics and I have received my education in French, a colleague had his in Portuguese, another in Mandarin, yet another in French/Arabic and our professors and PIs had theirs in German, English, French, Spanish and Romanian (that I know of, could be more).
You are right that at conferences people speak English, and we speak English in group meetings for the simple reason that it's the common denominator. There is no other reason. We have scientific discussions in French and English, some have them in German or Arabic, it doesn't matter because they're all equally capable of describing scientific thought.
I think the point you're trying to make is that the scientific vocabulary in some languages, in some scientific fields, sometimes doesn't keep up with that of English. This I would concede to you. But usually, just like English does, the other languages simply borrow the new words (or craft the usually obvious equivalents using greek/latin or whatever). This has nothing to do with a language's inherent capacity of describing concepts, as you maintain. This argument is a much weaker form than that which you propose.