Bless you
Seriously, I have no idea
Yes, that's how it sounds in my head - just like it's spelled Mange like the disease, tout like the tattle-tale. And so unappealing that way.
Yeah, it's French, so it's not pronounced the way it's spelt
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As someone said above, it means 'eat all' - 'manger' (mon-shay) means 'to eat' in French and 'tout' (too) means 'all'. Mange tout is 'monsh-too'.
Another example of manger being used here is the sandwich/coffee chain 'Pret a Manger' - 'pret a monsh-ay' (meaning literally 'ready/prepared to eat').
I suppose it can be compared to the way Spanish words are pronounced by non-Spanish speakers - like the correct pronounciation is 'torti-ya' not 'tortilla' and 'halapen-yo' not 'jalapeeno'.