There were many lingua francas of which French was supposedly the first global lingua franca. That changed and it became English (from what I understand). We will probably see another language become the lingua franca, so my question is: should it be English? Are there better candidates out there? Why / why not?
Question is, what should be the criteria for deciding which other language?
If it is for the sake of current global usability, English remains top.
If it is for geostrategic considerations, Spanish, French and Arabic would be the languages to cover South and Central America, large parts of Africa and West Asia.
If it is for population dominance inside the EU, it would be German, which probably will ruffle some feathers. If it is for population dominance in Europe, it should be Russian, which will ruffle a lot of feathers.