i find it quite interesting that you seem to be very comfortable with languages (english, french, programming) in their written forms, but less so verbally. i wonder whether it is linked to the parts of the brain used for visual comprehension rather than aural ; perhaps your neurons are more efficient there, or have more connections. however the guitar would seem to bely this, since learning guitar must be at least partially aural.
i think generally there tend to be specific areas in which a person may feel particularly comfortable or proficient, depending on the way they tend to apprehend the world and with what form of interaction with information / sensory stimuli they are most comfortable. i am generally quite comfortable with language for example. i am more or less equally comfortable in english and french (verbally and in writing) and things like html and css code come relatively easily to me and are easy for me to understand in a significant way. when i travel i can easily learn a few words simply by seeing or hearing them, and it is easy for me to detect similar words between languages, or words which might have the same root or origin as another word i know.
on the other hand, while letters and words "make sense" to me and seem to arrange themselves into comprehensible patterns without much of an effort, numbers remain more abstract. so for example, while i can do sudoku, i find it less appealing than a crossword or even a letter sudoku puzzle ("moji doku" : they have some of those online at this site :
http://www.tv5.org/TV5Site/cruci/mojidoku22.php), and whereas the letters in the moji doku will immediately form evident patterns for me, when i do a sudoku grill i have to verify the numbers i have used already individually.
it's very interesting also to notice the connections between apparently unrelated fields ; for example the first time someone told me that math and music are apprehended by the same part of the brain, i was very surprised.