Changing the language you think in, at least on some level (I don't know about deep grammatical structures, if that is relevant), isn't uncommon. I did this by choice, when I lived in Germany, as part of the exercise of acquiring the language. I think most people keep their native tongue for math. I did not, but my math skills are less than rudimentary, so this probably wasn't very different from other kinds of thinking. What seems unusual in Logwoods case is that, if I understood right, he adopted English as his "internal" language even though he was in a Hebrew-speaking environment.