My experience of this in French is that I usually get responses of "thanks, but please stop. You're ruining our language".
I'm sure speakers of other languages do this too, but the French do often seem to claim not to understand French spoken badly. I once asked a friend of mine, who is French, "Do the French really not understand bad French or do they just pretend not to?" The other people we were with reacted with horror - "You can't ask that!" I said I'm not being anti-French, I'm honestly interested to know.
I mean, if a French person walked up to you on the street in the UK and said something like "Excuse, I am wanting train to go", you would understand that they meant they were looking for the station. But in a similar situation the other way round you would likely be met with a blank look and a Gallic shrug.
Her response was "I've never really thought about it". That was the end of that, but then a year or two later she messaged me out of the blue with a screenshot of a book she'd been reading which was saying exactly the same thing - "the French do not like to hear their language spoken badly". She said "It seems you were right"!