1. A method for converting language input, the method comprising: at an electronic device having one or more processors and memory: obtaining text composed by a user; receiving, from the user, input comprising a sequence of symbols of a first symbolic system; determining a plurality of candidate word strings corresponding to the sequence of symbols, each candidate word string of the plurality of candidate word strings comprising two or more words of a second symbolic system; ranking the plurality of candidate word strings based on a probability of occurrence of each candidate word string of the plurality of candidate word strings in the obtained text; and displaying, based on the ranking, a portion of the plurality of candidate word strings for selection by the user.