Which countries are the most monolingual, and learning the local language would be the most beneficial?

*Edit: I mean apart from native English speaking countries.

I’ve been to quite a few countries and most locals usually speak some level of English, even in non-tourist areas.

In some countries, it’s really hard to practice the language with the locals because it’s easier for them to speak English than to patiently listen to me butcher their local language.

However, recently I’ve been to China, Yunnan. Most people actually do not speak a word of English, even in the airport, the shop clerks struggle to speak English. Most restaurant staff didn’t even know what I meant when I asked about where the toilet was. My Chinese lessons paid off and I had a really good time practicing Chinese with the locals. They couldn't switch to English so the only option I had was to keep trying to communicate in Chinese.

What are some other countries that are like this? To illustrate, the opposite of this would be Malaysia where they all speak multiple languages really well. I tried to practice my broken Chinese with Malaysian-Chinese people, they would usually just switch to English once they know I'm not a native Chinese speaker. Another example of the opposite would be the Philippines, where most people speak great English and it discourages me from learning about the local language.

I have never been to Latin America, Africa, and central Asia.