I'd like to ask is Mensa IQ test real, is Mensa even real. If so why are countries like Nigeria not a member, because there are a lot of smart people there who would like to join, like me for instance. Please give me your feedback.
The Mental Age tests are calibrated by country/culture:
Mental age is a concept related to intelligence. It looks at how a specific individual, at a specific age, performs intellectually, compared to average intellectual performance for that individual's actual chronological age (i.e. time elapsed since birth).(...) The score achieved by the individual is compared to the median average scores at various ages, and the mental age (x, say) is derived such that the individual's score equates to the average score at age x.
Mensa's criteria of "being in the top 2%" matches a proportion of the population for ANY measure of ANY criteria distributed in a normal distribution. If you label as "clever people" the "top 2%" of a population on a test measuring math, logic, vocabulary and visualization skills, by definition there are "clever people" in every country, and by definition also, they form 2% of the population.
Albeit one can join the Mensa International association, the objective is for members to gather and socialize for which national groups are more convenient (the name itself, "Mensa", means table (among other things)!):
Mensa means table in Latin as is symbolized in the organization’s logo. The organization says the word mensa has a triple meaning in Latin: mind, table and month, suggesting a monthly meeting of minds around a table. “The name chosen, according to the organization, to suggest a ’round table’ type group”. constellationsofwords.com/mensa
The fact that there is no Mensa national group and hence test in some countries (e.g. Nigeria, Chile, etc.) has more to do with the cost of creating and maintaining an association than with "having clever people", but people from those countries can join Mensa International with a mere IQ test from a psychologist of their country.
I hope it helps! (Beware of formulating your questions on stack exchange as debates: those questions will be very quickly closed, we aim to answer questions, not to be a forum for opinions.)