10. A computer-implemented method, comprising: under control of one or more computing systems configured with executable instructions, performing formant-based frequency warping on fundamental frequencies and coding spectrums of source speech waveforms in a first language to produce transformed fundamental frequencies and transformed coding spectrums; generating warped parameter trajectories based at least on the transformed fundamental frequencies and the transformed coding spectrums; and producing transformed target speech waveforms with voice characteristics of the first language that retain at least some voice characteristics of a target speaker using the warped parameter trajectories and features from target speech waveforms of the target speaker in the second language; training models based at least on the transformed speech target waveforms; and generating synthesized speech for an input text using the trained models.
10. A computer-implemented method, comprising: under control of one or more computing systems configured with executable instructions, performing formant-based frequency warping on fundamental frequencies and coding spectrums of source speech waveforms in a first language to produce transformed fundamental frequencies and transformed coding spectrums; generating warped parameter trajectories based at least on the transformed fundamental frequencies and the transformed coding spectrums; and producing transformed target speech waveforms with voice characteristics of the first language that retain at least some voice characteristics of a target speaker using the warped parameter trajectories and features from target speech waveforms of the target speaker in the second language; training models based at least on the transformed speech target waveforms; and generating synthesized speech for an input text using the trained models. 11. The computer-implemented method of claim 10 , further comprising receiving input text from a text-to-speech application or a language translation application.