Hi!
Zambia, Tanzania, Kenya, etc. are all different countries, with different CAAs with different rules.
I'm not sure what the rules are for Tanzania, as I am licensed in Kenya.
Validation and Conversion are two different things. Validation is where the CAA lets you fly on your home country license, typically for a limited time period. Conversion is where they use your home country license to give you a full new license from the respective CAA. Conversion is much more difficult, time consuming, and costly, typically. Some places will not do, or strongly prefer not to do a Validation.
In my experience, a Validation will work on an airplane that is not licensed in the country you are flying in (I had a Kenya Validation to fly a plane licensed in Sao Tome). A Conversion is needed to fly a native plane (I got a Kenya Conversion to fly a plane licensed in Kenya).
You will need a license, medical, radio license, and an instrument check to get a full Conversion to the new country's license. Converting an ATP is much better than converting a CPL, at least in Kenya.
cliff
NBO