This isn't even true in it's face. The lingua franca the term is derived from was a trading language across different cultures. It was used across the Mediterranean when there was a common language due to geopolitical or religious barriers. The need for such a language has only increased with increased global connectivity and global commerce. This is the same role it's filing in places like the EU, where only a small population speaks it natively, but it's a working language of the central bank and and the European Commission. In India and South Africa, it's lack of a native population has actually helped it maintain it's status, as other potential languages of commerce/government (for example Hindi in India and Afrikaans in SA) are associated negatively with nationalistic political movements for a majority of the population. Even in a country like Vietnam, where you would think a negative history with the United States would discourage it's use, over 50% of its population has some use of it. Overall, I just think it's hard to see any sort of trend of English lessening as a lingua franca.