2. An apparatus as claimed in claim 1, 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.
2. An apparatus as claimed in claim 1, 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. 5. An apparatus as claimed in claim 2, 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.