This would make for a really cool experiment. I study Mandarin Chinese, and yes, all varieties of Chinese (Mandarin, Yue, Wu, Min) are tonal, along with Vietnamese and Thai and others. It's been about 5 years since I've tasted DiPT but in the TIKHAL entry on it, it talks about an experiment done trying to measure how DiPT distorts audio perception and it was shown to have an alinear distortion effect:
(TIHKAL #4)
I have been told by an adventurous graduate student that a study has been made with two subjects who had absolute pitch, employing a piano and a sine-wave generator as a sound source. He wanted to explore the possibility that some relationship could be developed between the pitch of the note provided and the apparent pitch of the note perceived. No meaningful relationship was found, except for the reinforcement that the observed drop in pitch was not linear, in that true distortion rather than simple pitch dropping was always observed. Most interesting was the plot of the error for each note against the elapsed time. This provided what could be seen as an almost-quantitative measurement of the drug's intensity and chronology.
Hokkien Chinese dialects have 8 tones, whereas Mandarin only has 4. With Mandarin the tones are: rising, falling, down-up, and flat. Hokkien has those 4 + each are further distinguished by their range of pitch. I would imagine a language that had more discrepancies in the contour/tone of a word would be more likely to become garbled when on DiPT. It's important to note though too that tonal languages don't describe tonality in the same way the term is used in music theory. In music theory, a C note has a very specific resonant frequency which gives a sound it's recognizable identity whereas in language tonality is much more of a co-determinate relational identity. I've talked to many people who study music formally and don't use psychedelics who say that they can't hear the tones in the vocals in Mandarin music. I think it's because they are expecting to perceived a fixed resonant frequency of sound that can label something like a C note. but anyways.
I have also worked with Heimia salicifolia (sinicuichi) which actually gave me more pronounced auditory hallucinations than DiPT and would be also interesting to experiment with this plant and also with DiPT and tonal languages to see if a native speaker can still understand what's being said. How would you design such an experiment?