Ahhh it’s a lot easier to learn through immersion if you live there ;)
(A Brit who has lived in two other countries). I’m well aware of the resources on the internet. I’m also aware of the fact that this issue with the signs has bugger all to do with language barrier and everything to do with the people visiting being ignorant and inconsiderate tourists.
You are better off brushing up on the culture than you are the language. Simply looking at the sign through your phone camera would automatically translate it for you - yet another internet resource ;)
Eh… it’s probably not so much that they are demanding their language be spoken…
More a case of the tourists are probably being dickheads in general and the locals have had enough of their shit. That and the locals would like to be able to enjoy their own beach without having to wade through masses of tourists.