1. A method for text-to-speech conversion of a text in a first language comprising sections in at least one second language, comprising the steps of: converting said sections in said second language into phonemes of said second language; mapping at least part of said phonemes of said second language onto sets of phonemes of said first language; including said sets of phonemes of said first language resulting from said mapping in the stream of phonemes of said first language representative of said text to produce a resulting stream of phonemes; and generating a speech signal from said resulting stream of phonemes, wherein said step of mapping comprises: carrying out similarity tests between each phoneme of said phonemes of said second language being mapped and a set of candidate mapping phonemes of said first language; assigning respective scores to the results of said tests; and mapping each said phoneme of said second language onto a set of mapping phonemes of said first language selected from said candidate mapping phonemes as a function of said scores.