24. The system of claim 14 , wherein implementing the chimaera HMM based speech features generator comprises: transforming the implemented output HMM based speech features generator into the chimaera HMM based speech features generator by replacing each output HMM state model of the output HMM based speech features generator with the particular most closely matching set of generator-model functions; and speech-adapting the F0 statistics and the duration statistics of the transformed output HMM based speech features generator using the F0 transform and duration transform.
14. A system comprising: one or more processors; memory; and machine-readable instructions stored in the memory, that upon execution by the one or more processors cause the system to carry out functions including: implementing an output hidden Markov model (HMM) based speech features generator, wherein the output HMM based speech features generator comprises a first configuration of output HMM state models, each of the output HMM state models having a set of generator-model functions, and wherein the implemented output HMM based speech features generator is trained using speech signals of an output speaker speaking an output language; implementing an auxiliary HMM based speech features generator, wherein the auxiliary HMM based speech features generator comprises a second configuration of auxiliary HMM state models, each of the auxiliary HMM state models having a set of generator-model functions, and wherein the implemented auxiliary HMM based speech features generator is trained using speech signals of an auxiliary speaker speaking an input language; implementing a chimaera HMM based speech features generator that is the same as the output HMM based speech features generator, but wherein (i) the set of generator-model functions of each given output HMM state model of the chimaera HMM based speech features generator is replaced with a particular set of generator-model functions from among the auxiliary HMM state models of the second configuration that most closely matches the set of generator-model functions of the given output HMM, (ii) fundamental frequency (F0) statistics of the chimaera HMM based speech features generator are speech-adapted using an F0 transform that speech-adapts F0 statistics of the output HMM based speech features generator to match F0 statistics of the auxiliary HMM based speech features generator, and (iii) duration statistics of the chimaera HMM based speech features generator are speech-adapted using a duration transform that speech-adapts duration statistics of the output HMM based speech features generator to match duration statistics of the auxiliary HMM based speech features generator.