Considering that Dijkstra didn't consistently work in his native tongue (this is quoted from EWD498 which was written in English), this seems to be very much intentional.
I guess he meant: If you know how to formulate some concept efficiently in your native tongue, you can work out how to translate it into another [programming or human] language.
> If you know how to formulate some concept efficiently in your native tongue, you can work out how to translate it into another [programming or human] language
Even with that it seems strange, as I don't think I'm alone with having a easier time formulating some concepts (especially programming) in my now main language, while sometimes I can barely make myself understood when speaking my mother tongue.
The view yowlingcat offers in another sibling comment makes more sense to me, to not parse Dijkstras comment as literally as I did.
It's also possible that Dijkstra was wrong/didn't consider this case.
At this point in his career, he was still teaching in Dutch at a Dutch University, so likely had a different experience of being bilingual than you do.
I guess he meant: If you know how to formulate some concept efficiently in your native tongue, you can work out how to translate it into another [programming or human] language.