I, too, sometimes find that it is easier for me to express certain ideas in English than in my native language. However, I guess, in my case the reason seems to be analogous to the reasons mentioned in Steven Pinker's article "Why Academics Stink at Writing". Although it mainly talks about why academics find it difficult to express their ideas in simple words, it seems to me that if one uses predominantly English in certain settings or talking about certain subjects, then the reasons (chunking and functional fixedness) why ideas about these subjects are difficult to express in one's native language are probably similar.

Scholars lose their moorings in the land of the concrete because of two effects of expertise that have been documented by cognitive psychology. One is called chunking. To work around the limitations of short-term memory, the mind can package ideas into bigger and bigger units, which the psychologist George Miller dubbed "chunks." As we read and learn, we master a vast number of abstractions, and each becomes a mental unit that we can bring to mind in an instant and share with others by uttering its name. An adult mind that is brimming with chunks is a powerful engine of reason, but it comes at a cost: a failure to communicate with other minds that have not mastered the same chunks.

The amount of abstraction a writer can get away with depends on the expertise of his readership. But divining the chunks that have been mastered by a typical reader requires a gift of clairvoyance with which few of us are blessed. When we are apprentices in our chosen specialty, we join a clique in which, it seems to us, everyone else seems to know so much! And they talk among themselves as if their knowledge were conventional wisdom to every educated person. As we settle into the clique, it becomes our universe. We fail to appreciate that it is a tiny bubble in a multiverse of cliques. When we make first contact with the aliens in other universes and jabber at them in our local code, they cannot understand us without a sci-fi universal translator.

[...]

The second way in which expertise can make our thoughts harder to share is that as we become familiar with something, we think about it more in terms of the use we put it to and less in terms of what it looks like and what it is made of. This transition is called functional fixity. In the textbook experiment, people are given a candle, a book of matches, and a box of thumbtacks, and are asked to attach the candle to the wall so that the wax won’t drip onto the floor. The solution is to dump the thumbtacks out of the box, tack the box to the wall, and stick the candle onto the box. Most people never figure this out because they think of the box as a container for the tacks rather than as a physical object in its own right. The blind spot is called functional fixity because people get fixated on an object’s function and forget its physical makeup.

Now, if you combine functional fixity with chunking, and stir in the curse that hides each one from our awareness, you get an explanation of why specialists use so much idio­syncratic terminology, together with abstractions, metaconcepts, and zombie nouns. They are not trying to bamboozle their readers; it’s just the way they think. The specialists are no longer thinking—and thus no longer writing—about tangible objects, and instead are referring to them by the role those objects play in their daily travails. A psychologist calls the labels true and false "assessment words" because that’s why he put them there—so that the participants in the experiment could assess whether it applied to the preceding sentence. Unfortunately, he left it up to us to figure out what an "assessment word" is.

While scholars package their ideas and abstractions into chunks, in everyday language we package the connotations of words/idioms/expressions into similar implicit chunks that are hard to separate from the word/idiom/expression itself. Direct translation might not preserve all these connotations. It seems to me that while we could try to preserve some connotations that are most relevant in a given situation, we might feel uncomfortable doing so, because losing connotations feels like losing accuracy and precise meaning of what we tried to convey, even in situations where a simple paraphrase could preserve connotations that are actually relevant.

In a professional setting, functional fixedness becomes very important. It is probably the reason why so much professional jargon (outside the Anglosphere) is based on other languages, especially English.