1. A text-to-speech method executed by a processor for processing multi-lingual text message in a mixture of a first language and a second language into a multi-lingual voice message, cooperated with a first language model database having, a plurality of first language phoneme labels and first language cognate connection tone information and a second language model database having a plurality of second language phoneme labels and second language cognate connection tone information, the text-to-speech method comprising: separating the multi-lingual text message into at least one first language section and at least one second language section; converting the at least one first language section into least one first language phoneme label and converting the at least one second language section into at least one second language phoneme label; looking up the first language model database using the at least one first language phoneme label thereby obtaining at least one first language phoneme label sequence, and looking up the second language database model using; the at least one second language phoneme label thereby obtaining at least one second language phoneme label sequence; assembling the at least one first language phoneme label sequence and at least one second language phoneme label, sequence into a multi-lingual phoneme label sequence according to an order of words in the multi-lingual text message; producing inter-lingual connection tone information at a boundary between every two immediately adjacent phoneme label sequences, wherein every two immediately adjacent phoneme label sequences includes one of the at least one first language phoneme label sequence and one of the at least one second language phoneme label sequence; combining the multilingual phoneme label sequence, the first language cognate connection tone information at a boundary between every two immediately adjacent phoneme label of the at least one first language phoneme label sequence, the second language cognate connection tone information at a boundary between every two immediately adjacent phoneme labels of the at least one second language phoneme label sequence, and inter-lingual connection tone information to obtain the multi-lingual voice message, and outputting the multi-lingual voice message.