7. A non-transitory computer readable medium for causing a computer to perform operations for translating speech, the operations comprising: converting a speech of a first language to a source sentence of the first language by recognizing the speech using a speech recognition dictionary, the speech recognition dictionary storing words of the first language and pronunciation candidates corresponding to the words, and words of a second language and pronunciation candidates corresponding to the words; converting the source sentence to a translation sentence of the second language by using a translation dictionary, the translation dictionary storing words of the first language and translated words of the second language corresponding to the words; detecting an unknown word of the second language from the translation sentence by using the speech recognition dictionary, the unknown word being unregistered word not stored in the speech recognition dictionary; estimating a first pronunciation candidate of the unknown word from a character string of the unknown word included in the translation sentence by using Text-To-Speech technique; estimating a second pronunciation candidate of the unknown word from a pronunciation of an original word included in the source sentence, the original word corresponding to the unknown word; registering the unknown word, the first pronunciation candidate and the second pronunciation candidate, into the speech recognition dictionary correspondingly; and recognizing a next speech by using the speech recognition dictionary updated by the registering.
7. A non-transitory computer readable medium for causing a computer to perform operations for translating speech, the operations comprising: converting a speech of a first language to a source sentence of the first language by recognizing the speech using a speech recognition dictionary, the speech recognition dictionary storing words of the first language and pronunciation candidates corresponding to the words, and words of a second language and pronunciation candidates corresponding to the words; converting the source sentence to a translation sentence of the second language by using a translation dictionary, the translation dictionary storing words of the first language and translated words of the second language corresponding to the words; detecting an unknown word of the second language from the translation sentence by using the speech recognition dictionary, the unknown word being unregistered word not stored in the speech recognition dictionary; estimating a first pronunciation candidate of the unknown word from a character string of the unknown word included in the translation sentence by using Text-To-Speech technique; estimating a second pronunciation candidate of the unknown word from a pronunciation of an original word included in the source sentence, the original word corresponding to the unknown word; registering the unknown word, the first pronunciation candidate and the second pronunciation candidate, into the speech recognition dictionary correspondingly; and recognizing a next speech by using the speech recognition dictionary updated by the registering. 8. The non-transitory computer readable medium according to claim 7 , wherein the estimating a second pronunciation candidate comprises estimating a third pronunciation candidate of the unknown word from a speech sound included in the speech, the speech sound corresponding to the original word.