put it in another way, mostly indicates a usual practice, i.e. most of the time you would do something. for example, if you would walk on left side of a path 9 out of 10 times, you could say you mostly walked on the left side. almost, describes one specific episode, in which you are very much near the described outcome, but not exactly on it, e.g. I almost passed my examination, I scored 59. (= i failed the examination by 1 mark only)

Allow me to put it in English because I simply type English faster. Growing up in Hong Kong I believe that there is no best way of romanizing Cantonese. To complicate the matter further, although English is basically the only language utilizing roman alphabets that is taught in Hong Kong, the rather low phonological awareness in Hong Kong would mean that you would see a mixture of everything when you make a Hong Kong Chinese romanizing Cantonese words. Informal studies in universities, however, showed that among Yale, Jyutping, and Sidney Lau, more of Hong Kong Chinese are romanizing Cantonese words towards Sidney Lau's methods - and there is likely to be no coincidence that the former British colonial government of Hong Kong used Sidney Lau's method of romanization to teach British rulers Cantonese...

Just for your information, Bin Laden is translated as 拉登 in Cantonese.