I'm Khmer/Cambodian and I got a Khmer-English dictionary from my dad, published back in 1977 (it's actually during the genocide era)! In the preface page, there is this sentence reads:
I know Khmer is understudied (this Wikipedia article is great though), and I wanna get the opinions from outsiders.The compilers hope that the sometimes eccentric looking Khmer letters will not cause too much discomfort to users of the dictionary.