1. A method of selecting a word sequence for a text written in a language without word boundary marker, the method comprising: segmenting the text into a plurality of word sequences, each word sequence having at least one word segmentation unit that is different from the word segmentation units in other word sequences; determining a word boundary to be a common word boundary when a respective position of the word boundary after a word segmentation unit in a first word sequence of the plurality of word sequences is the same as a respective position of the word boundary after a word segmentation unit in a second word sequence of the plurality of word sequences; and selecting an optimal word sequence from one of a portion of the first word sequence that is before the common word boundary and a portion of the second word sequence that is before the common word boundary, at least one word segmentation unit in the portion of the first word sequence that is before the common word boundary being different from at least one word segmentation unit in the portion of the second word sequence that is before the common word boundary.