Licensing
Most countries have their own licensing authorities. The "biggies" are FAA/JAR ops licences and these entitle the holder to fly in/out world-wide control authority zones, as do most of the internationally recognised licences. You may hold as many licences as you wish although that would be a lot of extra work. If you already hold an officially recognised ATPL/CPL and you wish to gain or transfer to another licence type, it usually requires a minimum of an air law exam for the new state and sometimes a short sim/flight test. To fly for an airline in the M.E., FAA or JAR ops are acceptable but each airline will exam you subject to their own country's regulations; eg Saudi Arabia has its own licensing authority which is based on the FAA rules but has specific differences. I recommend you concentrate on getting licensed in your own country first; that will set you on your way.