Arabic gained international prominence because of the medieval Islamic conquests and the subsequent Arabization of the Middle East and North Africa, and it is also a liturgical language amongst Muslim communities outside the Arab World.
Standard Chinese is the direct replacement of Classical Chinese, which was a historical lingua franca in Far East Asia until the early 20th century, and today serves as a common language between speakers of other varieties of Chinese not only within China proper (between the Han Chinese and other unrelated ethnic groups), but in overseas Chinese communities. It is also widely taught as a second language internationally.
The major languages of the Indian subcontinent have numbers of speakers comparable to those of major world languages primarily due to the large population in the region rather than a supra-regional use of these languages, although Hindustani (including all Hindi dialects, and Urdu), Bengali and Tamil may fulfill the criteria in terms of supra-regional usage and international recognition. As an example, the native speaking population of Bengali vastly outnumber those who speak French as a first language, and it is one of the most spoken languages (ranking fifth or sixth) in the world with nearly 230 million total speakers, and is known for its long and rich literary tradition.
In addition to 370 million native speakers, English is estimated to have over 610 million second-language speakers, including anywhere between 200 and 350 million learners/users in China alone, at varying levels of study and proficiency, though this number is difficult to accurately assess. English is also increasingly becoming the dominant language of scientific research and papers worldwide, having even outpaced national languages in Western European countries, including France, where a recent study showed that English has massively displaced French as the language of scientific research in "hard" as well as in applied sciences.
During the 19th and early 20th centuries, French was the language of communication and diplomacy, and the favoured second language among the elite and the educated classes in Europe (including Russia, Romania, Bulgaria, Greece, and Ukraine) - as well as in many Middle East and North African countries such as Syria, Egypt, Ottoman Turkey and Iran. In addition, French enjoyed high status in some southeast Asian countries (Vietnam, Laos and Cambodia), and several South American ones like Argentina, Brazil, Chile, and Uruguay. However, French has declined steadily since World War I, being gradually displaced by English - although in Lebanon, Tunisia, Algeria and Morocco, French continues to be the favoured second language. Moreover, French still remains one of the working languages of many international organizations, including the United Nations, European Union and NAFTA. French is also internationally recognized to be of high linguistic prestige, still used in diplomacy and international commerce, as well as having a significant portion of second language speakers throughout the world.
German served as a lingua franca in large portions of Europe for centuries, mainly the Holy Roman Empire and later the Austro-Hungarian Empire. It remains an important second language in much of Central and Eastern Europe, and in the international scientific community.
Russian was used in the Russian Empire and the Soviet Union, and its teaching was made compulsory in the Eastern Bloc countries. However, the use and teaching of Russian has declined sharply in both the former Eastern bloc and the near abroad since the break up of the Soviet Union and Russia’s deputy education minister was quoted as saying in December 2013 that the number of Russian speakers had fallen by 100 million since that date. It is still widely spoken throughout the Caucasus, Central Asia, Eastern Europe and the Baltic states.
Russian is the largest native language in Europe, one of the six official languages of the United Nations, one of two official languages aboard the International Space Station and the third most widespread language on the Internet after English and German.
Spanish is the world's second-most spoken native language, after Mandarin Chinese. Spanish was used in the Spanish Empire and today is in use in Spain, in Latin American countries (except Brazil, French Guyana, Suriname, Guiana, Haiti and other Caribbean islands), and is spoken in many parts of the United States, particularly in Florida and the states which border Mexico. Indeed, by 2013 Spanish was the most widely taught non-English language in American secondary schools and schools of higher education. It is also an official language of the United Nations. As of December 2017 Spanish had the third largest number of internet users by language (after English and Chinese).