財政司=the Bureau of Finance is a single word,and so does司長=an official who is in charge of that department. 司司isn't a word, but maybe it's a nick name. We Chinese usually double a single character to address a certain people or thing. For example, 狗狗=doggie ,白白=a white dog's name, 佳佳=a girl's name, 喓喓=a bug's name for babies to learn. Seems like you failed to understand the structure of the proper noun. 香港特別行政區財政司司長=香港特別行政區的財政司的司長 香港特別行政區and財政司are both qualifiers for 司長. So that we would know the director is from Hong Kong instead of other places, and he or she is working in the fiancial bureau instead of other department.