Based on origin: the language(s) one learned first (the language(s) in which one has established the first long-lasting verbal contacts);
Based on internal identification: the language(s) one identifies with/as a speaker of;
Based on external identification: the language(s) one is identified with/as a speaker of, by others;
Based on competence: the language(s) one knows best:
Based on function: the language(s) one uses most.
Under some of these definitions, some African countries, including at least Angola, would qualify.
If you need a reference you can check the official report of the angolan 2014 census.
Section 7.1.10 (p. 51) shows that 71% of Angolans speak Portuguese at home. The same census show that Angola has 25.8 million inhabitants.
Nice idea, thanks!