After a few years flying in Japan and Africa I learned that the answer to your question is - It all depends.
For example, converting to Zambian licenses involved a cheesy technical exam and a $50 "examination fee" - payable in cash with no receipt, of course.
Botswana converted my FAA licenses after a very easy air law test for which the answers were widely available. Took about two weeks for them to do the paperwork.
Was trying to get a job flying for a South African company. Unique arrangement there where they had two levels of licenses - one allowed you to fly South African-registered aircraft but only OUTSIDE the country. This one was fairly easy to get - an air law test and some forms, I think. The other that let you fly them in the country was much more difficult to get involving some flight instruction, pricey course, etc.
Tanzania/Kenya. Buddies told me that converting your licenses there was straightforward if you had an ATP. It involved three or four months and a judicious application of "administrative processing fees" - cash, no receipt. Wink, wink. Nudge, nudge. These were pressing $1000 US in '99.
Japan? Abandon all hope all ye who try to convert your licenses here without the help of a company. Want an ATP? A friend was told that he would have to supply a light jet for the checkride. C172s were renting there for about $300 an hour at that time so do the math. Very possibly the must anally retentive system outside of Europe.
Pick your country and make your phone calls is about the only general rule that I know of. The good news is that alot of the world's aviation regulatory authorities are small and accessible unlike the behemoth that is the FAA.
Your bigger problem will be getting a work permit.