Apertium originated as one of the machine translation engines in the project OpenTrad, which was funded by the Spanish government. It was originally designed to translate between closely related languages, although it has recently been expanded to treat more divergent language pairs. To create a new machine translation system, one just has to develop linguistic data (dictionaries, rules) in well-specified XML formats.
Language data developed for it (in collaboration with the Universidade de Vigo, the Universitat Politècnica de Catalunya and the Universitat Pompeu Fabra) currently support (in stable version) the Aragonese, Asturian, Basque, Breton, Bulgarian, Catalan, Danish, English, Esperanto, French, Galician, Icelandic, Italian, Macedonian, Norwegian (Bokmål and Nynorsk), Occitan, Portuguese, Romanian, Spanish, Swedish and Welsh languages. A full list is available below. Several companies are also involved in the development of Apertium, including Prompsit Language Engineering, Imaxin Software and Eleka Ingeniaritza Linguistikoa.
Apertium is a shallow-transfer machine translation system, which uses finite state transducers for all of its lexical transformations, and hidden Markov models for part-of-speech tagging or word category disambiguation. Constraint Grammar taggers are also used for some language pairs (e.g. Breton-French).