As an English person I don’t think I would describe the sound in those words as zh.
Measure would be Meh sure don’t know phonetic sounds but basically it’s definitely an sh sound to me
Ration is a different sound to me but it’s difficult to explain maybe more like a longer shhhh sound.
I think to a British English speaker we don’t hear it as a z sound.
I hear it as a sh sound, so spelling it zh feels counter intuitive to me.
If a word was spelled meazhure I would be inclined to read it as mezz-hure my brain would separate the z and the h. They are two letters that do not work together.
The historical reason will almost certainly be related to Latin and french and I’m sure some people can add more but I just wanted how 9dd it sounds to me to describe it as a zh sound I do not hear a z sound in those words.
Maybe it’s an American English thing?
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