Later Lingua Franca
German, or a form of it, was the lingua franca of the Holy Roman Empire, from the time of Charlemagne to the 16th century. After that, it was still considered the language of science well into the beginning of the 20th century, along with some remnants of Latin nomenclature. Some scientific literature is still published simultaneously in English and German. After WWII, German became less politically correct, and more and more work which would have been published only in German was published jointly in German and English, or only in English.
French was the preeminent language of diplomacy from the 17th century until the Treaty of Versailles, in the 20th century, when the Treaty was written both in English and French. It was used internationally for so many purposes that it is still of great importance in international organizations, and of the six languages that are the official languages of the United Nations, it is French and English in which most international documents are written. French was also the language of literature and letters as Latin grew less used.
Spanish grew in importance in the period of world colonization, and still is a lingua franca throughout most of Central and South America, as well as some of the other former Spanish colonies in Africa and some of Asia. As well, it continues to become of greater importance in the United States, as a growing percentage of the American population speaks Spanish as a native tongue.
Russian was the lingua franca of the USSR, of the Soviet Union - used throughout all the different countries in the USSR. Since the breakdown of the Soviet Union, the number of official speakers has dropped drastically, although that may also be a political decision. It is no longer accepted as the sole lingua franca of the former Soviet Union, and many countries have resorted to English rather than use Russian to communicate between different nations. Some scientific material is also published simultaneously in both Russian and English, and Russian continues to be a presence on the Internet.
Chinese, or its various dialects, was the lingua franca of Asia, and again is as important as it was in the time of the Mandarin Empire. It also is spoken natively by more people than any other language. Through the sheer numbers of people speaking Mandarin and other Chinese dialects, it is growing in significance as a language on the Internet.
Hebrew, which is not a language spoken by a huge portion of the world's inhabitants, remains a lingua franca, as it has since the time of the Romans, and the diaspora of the Jews. It spread throughout Europe and the Middle East as a way for Jews in different countries to communicate with one another despite the languages of the many countries where they were born. It has also stayed important in its role as a lingua franca because of its religious significance.