Thai – the world’s most complicated language? Something we’ve suspected for years and reassuring for our mental capacities! The VDO is referring to written Thai but it’s certainly hard enought just to speak it! Basically, if we’ve understood correctly it’s to do with Thai language having 5 tones and, unlike most tonal languages, those tones being incorporated into the writing system, as well as it employing unreconstructed spelling and grammar from an ancient language that died out centuries ago. (Yes Vietnamese employs tonal markers but at least they use a Latin alphabet whilst the incredibly complex looking Khmer alphabet has no tones at all!)
So…something akin to trying to write modern English using only a 2,000 year old Latin writing system! Good luck!