14. A method as claimed in claim 13, characterized in that each target hypothesis comprises a series of target words selected from a vocabulary comprising words in the second language and a null word representing the absence of a word.
14. A method as claimed in claim 13, characterized in that each target hypothesis comprises a series of target words selected from a vocabulary comprising words in the second language and a null word representing the absence of a word. 17. A method as claimed in claim 14, characterized in that: the translation match score for a target hypothesis comprises the product of the word match scores for the target hypothesis and the source words in the input series of source words; and the target hypothesis match score for a target hypothesis comprises the product of the language model match score for the target hypothesis multiplied by the translation match score for the target hypothesis.