In the Middle Ages, in Europe, educated people, i.e. those who learned to read and write, learned to read and write (and speak) Latin, whatever their native language might be. This meant that educated people across the whole of Europe could talk and exchange ideas using Latin.
With the rise of nationalism (or was it earlier than that?), people started to read and write in their various native languages and Latin became sidelined, so losing the former ease of international discourse.
These days, another language has grown up to replace Latin, namely English. Educated people across Europe (and the rest of the world?) now all learn English as a second language. So English is becoming the new Latin.
As one who regularly works with non-native English speakers, my experience is that English is not the Lingua Franca you suggest. Perhaps many people learn it, but their facility with the language is often lamentable. Personally, I favour the introduction of an InternationalAuxiliaryLanguage? for enhanced communication (e.g. LojbanLanguage), but inertia is a sociological phenomenon as much as a physical one.
One of the tricks in learning a new language is immersion in the language's culture: reading books, newspapers, magazines and watching their movies and tv shows. Latin, technically a dead language, has two sources of culture to draw from: Ancient Rome and the Catholic Church. That's probably the reason there are more KlingonLanguage speakers than LojbanLanguage speakers.
Very likely true. This isn't the place to get into a debate about which language to choose for an InternationalAuxiliaryLanguage? - there are, after all, thousands to choose from. My experience is that KlingonLanguage is severely limited in its expressive power, EsperantoLanguage is very much a regularized IndoEuropeanLanguage, LojbanLanguage is simply weird, and none have particularly good source material for gaining mastery. (I trust that is a sufficiently balanced viewpoint/summary).
But a LinguaFranca is usually a reduced subset of the original. The problem with English arises when fluent native speakers are communicating with reasonably fluent non natives, who miss nuances and/or idioms. But communication between groups of non native speakers works well e.g. Swedes and Germans. -- AonghusOhAlmhain
Another interesting effect is that these languages all attempt to be culturally neutral. Yet, the more material is generated for a ConLang, the more of a culture it acquires. It may be a unique culture, but it is nonetheless a culture all to its own. Thus, cultural neutrality is a myth that should not be strived for. This is why the Indo-European centric nature of EsperantoLanguage does not bother me one wit. -- SamuelFalvo?
Someone once said that the new world language is English as spoken by non-native speakers. There are far more people in the world who have English as their second language than who have it as their first. -- SoerenMors?
An important point! Some implications are discussed on EnglishLanguagePrescriptiveness.
Also, please see the discussion of American English as the potential universal spoken language of the entire race on EnglishPleaseDiscussion. Perhaps that whole discourse could be moved to a page better supported by spoken language experts? Something that compares the relative values of modern languages?
Another tangent to Aonghus' point is that non-native variations of a language often gives birth to new languages. That's how Latin became the Romance languages. See VulgarLatin for a discussion of how that happened. --NickBensema
FWIW, I've heard it quoted that English is the most common second language and French is the second most common second language. I'm fluent in the first and I can get by in the second, and between the two, I've been able to communicate in several bits of Europe and Russia (primarily in English although the few times people didn't speak English, they spoke French). This is mildly bizarre to me, but I suppose that there's some holdover from when French was the "Royal language" and it was considered civilized to learn it. -SeanDuggan?
See: ConLang, ChoosingaConLang and pages therefrom.