When the Russian pilot of an Aeroflot jet is approaching Moscow's airport staffed by Russian Air Traffic controllers, convention still holds that everybody is speaking English. Even if that English isnt great, there is still enough to know that the basics can be covered. This is necessary because there isn't a lot of time to react, negotiate language, etc. and, since aviation really "took off" first in English speaking countries, the precedent eventually became standardized and the safety and efficiency benefits were realized.
Going back to my "private sailboat enters a foreign harbor" thing, can I expect the same treatment in a boat? I'm thinking that it would be really easy to ask for customs if I could assume that the Harbor master or some other official could be counted on to speak English. Otherwise, it would be wise to bring along a dictionary.
So, is there an international language of the sea that can be counted on.