=General sense= The term lingua franca (the name comes from the historical sense) refers to a language most widely used: adopted as a common means of communication between people of different languages. English is the current lingua franca of the world, and people worldwide are fast becoming acclimated to its use. Despite superficial differences, such as accents, an overall proficiency in English is steadily growing. Accents simply bear the tonal qualities of the regional dialects. India, for example, speaks with a distinct accent, yet maintains a high level of literacy and proficiency.
In the past Koine Greek, Latin and French served as a lingua franca in the Western-dominated world. In some regions of the world, there are other languages that perform this function; for example, Swahili in Eastern Africa, Hindi in most of India, Bislama in the Pacific Islands, and various other Pidgin languages in other locations, and times.
Esperanto and Ido are constructed languages that some people propose as a replacement for English as the global lingua franca. Their supporters argue that a lingua franca should be as simple as possible, while still being highly expressive. They claim that English and other natural languages, being ethnically derived, are not suitable for a common language, since each ethnic language contains caveats and idiosyncracies that hamper their ability to be learned, and since ethnic languages confer an automatic advantage to native speakers in interaction between native speakers and non-native speakers.
Constructed languages tend to base their premise of universality on the assumption of a need for extreme simplicity, and the premise that non-native speakers should not be at a disadvantage. Their advocates claim that idiosyncratic elements as presented in ethnic languages are a major obstacle to a functional degree of use in that language. Unfortunately some learning curve still applies to constructed languages; and as such, their use is still rare.
According to advocates of constructed languages, the number of speakers is no measure of the intrinsic value of a constructed language. If a constructed language (or other language with few speakers) were to be decided upon such as by international agreement to be used as an international auxiliary language, the number of speakers would rise to meet the demand. At present, the demand for speakers of constructed languages is limited, though Esperanto is said to have gained currency as a lingua franca among translators.
=Historical sense= Lingua Franca (Italian meaning "Frankish language") or Sabir ("to know") was an early pidgin language, used in the Mediterranean area from the 14th century or earlier and still in use in the 20th century.
It had a heavy influence of Romance languages, especially Italian dialects.
It was the language used between slaves and their captors in the bagnio of Algiers.
According to the monogenetic theory of the origin of pidgins pioneered by Hugo Schuchardt, Lingua Franca was known by Mediterranean sailors including the Portuguese. When Portuguese started exploring the seas of Africa, America, Asia and Oceania, they tried to communicate with the natives by mixing a Portuguese-influenced version of Lingua Franca with the local languages. When English or French ships came to compete with the Portuguese, the crew tried to learn this "broken Portuguese". Through a process of relexification, the Lingua Franca and Portuguese wordstock was substituted by the languages of the peoples in contact.
This theory explains the similarities between most of the European-based pidgins and creoles, like Tok Pisin, Papiamento, Krio, Chinese English Pidgin. These languages use forms similar to sabir for "to know" and piquenho for "children".
Lingua Franca left traces in today's Algerian slang and Polari. Polari from Italian parlare ("to talk") was a cant used by London variety artists and gays.
English words like "savvy" (from sabir) and "pickanniny" can be traced to Lingua Franca.
