Do you think primarily in English?
dimitar: I think in the language that I am using or have experience on the subject - my native language is Bulgarian, but sometimes I think in an another language when I face a concept I experienced in another language. Those cannot be only natural languages but also formal ones - its too confusing and slow to translate mathematical, psychics, programming or any notation into a natural language.I sometimes only know English terminology on a subject and I am forced to think and even use English words.. I consciously try to avoid that. Usually people with only ostensible knowledge of English AND the subject pollute their native language with unnecessary foreign words. Unfortunately those people are very common here and annoy me daily, but on the other hand its fairly easy to separate the signal from the noise by looking at how often such fancy words are used.I really recommend this essay in which the unnecessary use of foreign words is only part of a bigger problem: 
George Orwell, "Politics and the English Language," 1946