1. A computer-implemented method of speech recognition by adding a new sentence to a word-level finite state transducer (FST) having a plurality of states and connecting arcs, the method comprising: determining, using a computer processor, an existing prefix subset of states and arcs in the FST matching a prefix portion of the new sentence; appending a new sequence of states and arcs to the FST corresponding to a remainder of the new sentence after the prefix portion; determining an existing suffix subset of states and arcs in the FST corresponding to a suffix portion of the new sentence; connecting the portion of the new sequence before the suffix portion to the suffix subset to create a modified FST including the new sentence and not satisfying global optimization criteria; and storing the modified FST in memory and dynamically expanding the modified FST using a computer configured as a compiler and using the modified FST for speech recognition, text-to-speech, and/or text processing.