In Spain, one is told to say ’patata‘. I don’t get that one either.
I suppose every language has its own ‘stretch mouth in grin’ word for the photographers.
In Spanish, they don’t really have long vowels, so instead of the long ‘-ee-’ in the middle of cheese, they repeat their very open but short ‘a’ three times in ‘patata’. The internal t’s don’t change the wide open shape of the mouth.
Be interesting to hear what other languages do say here! Disappointingly, the Dutch are so well versed in English many have taken over the ‘cheese’ word too! I always say ‘say kaas’, as this word (a) means ‘cheese’, and (b) has a nice long open vowel which also serves the purpose.
Can’t remember it in French off hand...?