The purpose of the Security Council is to provide for balanced, representative involvement and through this, to contribute to the achievement of "world peace enforcement".
Tp achieve this, the UNSC must comprise an effective grouping of: 1) the world's leading nations; 2) most powerful nations; 3) most politically influential nations; 4) most economically developed nations; and 5) the largest nations, measured by population, cultural, or religious groupings.
France would not qualify, due to its limited impact, culturally, politically, militarily, or organisationally, beyond France and the French common community based around Cote d' Ivorie and Sierra Leone in Western Africa.
Culturally, the French language also suffers because of the growing reach of English (as the official language of business, global commerce, international transportation, of the internet, and of 2nd choice in those countries where English is not the 1st language).
French is rarely practised or spoken outside of France. Conversely, Spanish is the world's fastest growing language, followed by English.
Politically, France's position as a permanent member of the UNSC was more of a historical vagary. In WW2 (from out of which, the UN system was ultimately developed), the 3 main allied powers were the USA, Russia, and the UK.
It was more out of deference to the contribution of the Free French forces of Charles de Gaulle that contributed more to France's inclusion in the shaping of post-WW2 Europe. If, however, it had been left to reality, the actions of the Vichy, during and throughout the German occupation, would have put paid to any lasting French participation if a post-war Europe.
Global French political and diplomatic influence has been waning for >200 years, ever since the battlefield defeats suffered by Napoleon, etc. At least for the UK, the Commonwealth still exists as the largest global union, outside of the UN system, and the ONA (Organistaion of non-aligned States).
China's participation in the UNSC owed much to the legacy created by Chiang Kai-shek and the Nationalist forces that he led in China, prior to evacuating to Taiwan in 1949.
Had have the UN system and the UNSC been established in the early 1950s, then it is doubtful that communist China would ever have received permanent member status before the UNSC (at least, in the formative years).
As for including South Africa, this is because South Africa is the major strategic power in Africa. It is also the most economically and industrially developed of the African powers and currently accounts for >10% of all African generated GDP.
Nigeria's population of 115m in 2000 is expected to increase to 177m+ by 2020, and to >300m by 2050. So, on the basis of population size, geo-political positioning in the near-central African region, and a growing /developing economic and industrial base, Nigeria should qualify for permanent membership.
By 2050, 8 (currently existing) countries will comprise >1/2 the world's population* - India (1.0b in 2000, to 1.32b by 2020), China (1.275b, to 1.43b), Pakistan (143m to 227m), Nigeria (115m to 177m), the United States (285m to 345m), Bangladesh (138m to 195m), Ethiopia (66m to 105m) and Congo (49m to 84m).
[* = medium variant analysis, World Population Prospects: The 2002 Revision and World Urbanization Prospects: The 2001 Revision, Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat, http://esa.un.org/unpp]
In Africa, Nigeria is more developed, and more politically stable than either Congo, or Ethiopia. It's population is also greater than the combined population of both of these countries (actual and prospective). Nigeria is, however, less economically developed than "the super 10" South Africa which accounts for >10% of "whole of Africa" GDP.
