1. A machine translation method for translating source text from a first: language to target text in a second language, comprising: receiving the source text in the first language; accessing a library of bi-fragments, each of the bi-fragments including a text fragment from the first language and a text fragment from the second language, at least some of the bi-fragments being modeled as elastic bi-fragments in which words of a fragment are spaced by a gap which is able to assume a variable size corresponding to a number of other words which are to occupy the gap; retrieving text fragments from the second language from the library corresponding to text fragments in the source text; generating at least one target hypothesis, each of said target hypotheses comprising text fragments selected from the second language; and evaluating the target hypothesis with a translation scoring function which scores the target hypothesis according to a plurality of feature functions, at least one of the feature functions comprising a gap size scoring feature which favors hypotheses with statistically more probable gap sizes over hypotheses with statically less probable gap sizes.