13. The system of claim 9 , wherein building the speech to text decoder according to the previously obtained acoustic model, the respective template-based language model, the respective class-based language model and the respective lexicon-based language model for the given field, and the data samples further comprises: obtaining an expanded class-based language model for the given field by expanding the respective class-based language model using one or more sentences obtained through combining one or more templates from the respective template-based language model and one or more words from the respective lexicon-based language model; and building the speech to text decoder based on the expanded class-based language model and the lexicon-based language model for the given field, and the data samples.
13. The system of claim 9 , wherein building the speech to text decoder according to the previously obtained acoustic model, the respective template-based language model, the respective class-based language model and the respective lexicon-based language model for the given field, and the data samples further comprises: obtaining an expanded class-based language model for the given field by expanding the respective class-based language model using one or more sentences obtained through combining one or more templates from the respective template-based language model and one or more words from the respective lexicon-based language model; and building the speech to text decoder based on the expanded class-based language model and the lexicon-based language model for the given field, and the data samples. 14. The system of claim 13 , wherein building the speech to text decoder according to the previously obtained acoustic model, the respective template-based language model, the respective class-based language model and the respective lexicon-based language model for the any given field, and the data samples, further comprises: performing weighted finite state transduction on the respective class-based language model in the given field, to obtain a respective class-based language model WFST (Weighted Finite State Transducer); performing weighted finite state transduction on the respective lexicon-based language model in the given field, to obtain a respective class vocabulary WFST; performing weighted finite state transduction on the respective class-based language model WFST and the respective class vocabulary WFST in the given field, to obtain a fused language model WFST; performing weighted finite state transduction on the data samples, to obtain a respective vocabulary WFST; performing weighted finite state transduction on the vocabulary WF ST and the fused language model WFST, to obtain a vocabulary language WFST; performing weighted finite state transduction on the acoustic model, to obtain an acoustic model WFST; performing weighted finite state transduction on the acoustic model WF ST and the vocabulary language WFST, to obtain an ultimate WFST; and taking the ultimate WFST as the speech-to-text decoder in the given field.