French Sign Language (langue des signes française or LSF) is the sign language of the deaf in the nation of France. According to Ethnologue, it has 50,000 to 100,000 native signers.
French Sign Language is related to Dutch Sign Language (NGT), German Sign Language (DGS), Flemish Sign Language (VGT), Belgian-French Sign Language (LSFB) Irish Sign Language (ISL), American Sign Language (ASL), and Quebec Sign Language (LSQ).
The methodical signs he created were a mixture of sign language words he had learned with some grammatical terms he invented. The resulting combination, an artificial language, was over-complicated and completely unusable by his students. For example, where his system would elaborately construct the word "unintelligible" with a chain of 5 signs ("interior-understand-possible-adjective-not"), the deaf natural language would simply say "understand-impossible". LSF was not invented by the abbé, but his major contributions to the deaf community were to recognize that the deaf did not need spoken language to be able to think, and to indirectly accelerate the natural growth of the language by virtue of putting so many deaf students under a single roof.
French Sign Language flourished from this point until the late 1800s at which point a schism between the manualist and oralist schools of thought had long developed. In 1880 the Milan International Congress of Teachers for the Deaf-Mute convened and decided that the oralist tradition would be preferred. In due time, the use of sign language was treated as a barrier to learning to talk, and thus forbidden from the classroom.
This situation remained unchanged in France until the late 1970s, when the deaf community began to militate for greater recognition of sign language and for a bilingual education system. In 1991 the National Assembly passed the Fabius law, officially authorising the use of LSF for the education of deaf children. A law was passed in 2004 fully recognising LSF as a language in its own right.