I am afraid that what blabla says is confirming what I wrote and this is correct: your validation is only good for as long as your JAA licence is current, which means your rating, medical, etc must stay current. As the airline will not be able to use you once your currency is gone, they either use this initial period to get you the local licence or they have a JAA TRE on staff, as some African companies do (there are JAA approved TRTOs and sims in Africa), or they send you straight to a JAA TRTO.
So this is definitely not a question of whether you are in JAA land or not, but if you have a JAA TRE in an acceptable sim.
A licence is generally valid for 5 or 10 years, so there is no problem.
JAA class 1 medical can be done in many countries outside JAA land, not sure about Africa though (did mine in the Caribbean).
Again: your rating will not expire if you do the annual LPC, this (depending on your CAA) will NOT have to be a JAA TRE, my CAA has accepted a local ICAO TRE with the restriction as per my first post.
Upon commencing work with a JAA carrier at a later stage, you will have to do their LPC anyway, and this will remove the limitation, but this has nothing to do with currency.