4. The device according to claim 3 , further comprising: a semantic category dictionary storage unit configured to store therein a semantic category dictionary in which words are associated with semantic categories of the words, wherein, when the speech is of the first language, the search unit compares the semantic categories of a plurality of words forming the first character string with the semantic categories of a plurality of words forming the sentence of the first language stored in the parallel translation storage unit and searches for sentences in the first language similar to the first character string, and when the speech is of the second language, the search unit compares the semantic categories of a plurality of words forming the second character string with the semantic categories of a plurality of words forming the sentence of the second language stored in the parallel translation storage unit and searches for sentences of the second language similar to the second character string.
3. The device according to claim 1 , further comprising: an input receiving unit configured to receive an input of a speech uttered in the first language or the second language; a recognition unit configured to, when the speech is of the first language, recognize the speech and generates a first character string of the first language, but when the speech is of the second language, recognize the speech and generates a second character string of the second language; and a search unit configured to search for sentences in the first language similar to the first character string from the parallel translation storage unit when the speech is of the first language, and search for sentences in the second language similar to the second character string from the parallel translation storage unit when the speech is of the second language, wherein, when the speech is of the first language, the display unit displays the first character string and the searched sentences in the first language as the next utterance candidates of the first sentence in the first language, but when the speech is of the second language, the display unit displays the second character string and the searched sentences in the second language as the next utterance candidates of the first sentence in the second language.