1. A computer-implemented method for generating a multilingual acoustic model for use in a speech recognition system, comprising: providing to a processor from memory a main acoustic model including a set of probability distribution functions and a probabilistic state sequence model; providing to the processor from memory at least one second acoustic model including a set of probability distribution functions and a probabilistic state sequence model; in a computer process, replacing each of the probability distribution function of the at least second acoustic model by one of the probability distribution functions from the main codebook and/or each state of the probabilistic state sequence model from the second acoustic model by a state of the probabilistic state sequence model from the main acoustic model based upon a criteria set to form a modified second acoustic model; and in a computer process, combining the main acoustic model and the at least one modified second acoustic model to form the multilingual acoustic model.