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. 12. The computer-implemented method of claim 10 , further comprising: estimating the coding spectrums of the source speech waveforms using a Speech Transformation and Representation using Adaptive Interpolation of Weighted Spectrum (STRAIGHT) speech analysis; extracting the fundamental frequencies of the source speech waveforms using pitch extraction; and obtaining linear spectrum pairs (LSPs) from the transformed coding spectrums, wherein the generating further includes generating the warped parameter trajectories base at least on the transformed coding spectrums and the LSPs.