14. A statistical machine translation system that adapts translation according to context, the system comprising a processor with a memory having program instructions for: defining a source text unit and a translation unit with respect to a source text to be translated; constructing a specialized translation mapping for the source text unit, the specialized translation mapping provided by adapting a language model of the system, a translation model of the system, or both; and using the specialized translation mapping to carry out the translation of the translation unit; where, if the language model is adapted, the system further comprises program instructions encoding an adaptive language model that includes a language model in the target language associated with each of a plurality of clusters of the bilingual document pairs, and where, if the translation model is adapted, the system further comprises program instructions for: encoding a plurality of joint count tables, each associated with a respective bilingual document pair or cluster of bilingual document pairs that translate the aligned words or aligned phrases similarly; and defining a similarity measure to map an arbitrary source text unit to a weighted combination of the joint count tables, where joint count tables corresponding to source language of the bilingual document pairs that are more similar to the source text unit are assigned greater weights, and joint count tables corresponding to source language of the bilingual document pairs that are more dissimilar from the source text unit are assigned lower weights; whereby the machine translation system is adapted to apply at least one of the adaptive language models, or the weighted combination of the tables, to carry out translation of a translation unit based on similarity of the source text unit associated with the translation unit to the source document pairs, or clusters.
14. A statistical machine translation system that adapts translation according to context, the system comprising a processor with a memory having program instructions for: defining a source text unit and a translation unit with respect to a source text to be translated; constructing a specialized translation mapping for the source text unit, the specialized translation mapping provided by adapting a language model of the system, a translation model of the system, or both; and using the specialized translation mapping to carry out the translation of the translation unit; where, if the language model is adapted, the system further comprises program instructions encoding an adaptive language model that includes a language model in the target language associated with each of a plurality of clusters of the bilingual document pairs, and where, if the translation model is adapted, the system further comprises program instructions for: encoding a plurality of joint count tables, each associated with a respective bilingual document pair or cluster of bilingual document pairs that translate the aligned words or aligned phrases similarly; and defining a similarity measure to map an arbitrary source text unit to a weighted combination of the joint count tables, where joint count tables corresponding to source language of the bilingual document pairs that are more similar to the source text unit are assigned greater weights, and joint count tables corresponding to source language of the bilingual document pairs that are more dissimilar from the source text unit are assigned lower weights; whereby the machine translation system is adapted to apply at least one of the adaptive language models, or the weighted combination of the tables, to carry out translation of a translation unit based on similarity of the source text unit associated with the translation unit to the source document pairs, or clusters. 18. The system of claim 14 further comprising program instructions for dynamically constructing a development corpus based on its similarity to the source text unit.