I spent some time on a research project examining spectrograms and coding vowels for speakers of American English from a few rural regions in the state of Oklahoma.
I noticed that certain speakers seemed to consistently target 3 separate peaks (or articulator positions) on certain vowels, such as the /ɛ/ in a word like /hɛn/ (and to my ear such vowels sounded noticeably different than the English varieties from my AE region). While I expected to find diphthongs among the data sets, it really surprised me to find a hint of triphthongs in an English variety. I didn't find much research out there on whether that is actually some sort of a diphthong-glide combination or a "real" triphthong (where the speaker has 3 distinct target areas for the vowel), and I suspect that it is a very limited situation in English, and not a clear example of triphthongs.
What I really wondered after the project was if there are languages where triphthongs are a regular feature? Could someone please tell me an example of a language or dialect that contains triphthongs? I would love to know. Thank you!