Unlike for example Chinese with its extremely complicated writing system and four “pitched tones” and a “toneless tone”, I think that English is a suitable candidate for a new lingua franca because basic English is much easier to learn than for example basic Chinese, basic Russian, or even basic German or French. Unlike in German, all nouns and adjectives have only one case, you don’t have to learn a great number of conjugation classes for verbs as you would have to in Russian, etc. According to some linguists, the simplicity of basic English is probably due to the fact that after the Viking raids on England, complicated features in the grammar of Old English were replaced by simpler forms by the Vikings who stayed in England. The Vikings were good at many things, but not really very good at languages, says John McWhorter in his book What Language Is, which makes perfect sense to me.
By necessity, a lingua franca becomes simplified and modified by people who use it for communication with other people whose first language is also different from the lingua franca. Chinese characters were written in a slightly different manner in classical Vietnamese and classical Japanese (文語, bungo), and thanks to Mao, there is a big difference now even between the simplified Chinese characters in Mandarin and traditional Chinese characters. People whose first language is not English often understand better other people who speak English but also are not native speakers of the language. As a former European, I think that either of the major European languages, by which I mean English, French or German, would be a suitable candidate for a vehicle for communication among people who speak different languages.
I don’t think that Chinese or other complicated languages have a shot at replacing a much simpler language such as English in this role, no matter how much the US is in debt to China. As a Czech friend of mine who himself speaks fairly fluently 4 languages told me once, “Bad English is the most useful language in the world. Everybody speaks it”.
Although the American Empire is probably in its final period of unstoppable decline, just as the Roman Empire, the British Empire, the Soviet Empire, etc., were quickly sinking in their time when the greed and stupidity of the ruling class in those empires finally just about ruined everything, the English language is in my opinion one cultural characteristic of the Anglo-American culture that is worth preserving.
Eventually, the lingua franca that English has become will be replaced by another language, and it will not take eight hundred years, which is for how long Latin was used in this role.
But I have absolutely no idea which language it will be. Possibly some bastardized version of English mixed with Chinese or German or another language, or vice versa, that is if people are still living on this planet a few centuries from now, which seems unlikely at this point.
It is also quite possible that historians and linguists in a scientific expedition of visitors from space who study alien civilizations will write in their history books describing the fate of our civilization that at the end of a civilization on a planet called Earth in English, the last lingua franca on that particular planet was a simplified version of a language called English.