I've seen quite a few people with my own eyes use devices with an English interface (or French) without knowing much English (or French). Some of them are illiterate. This is quite common in some parts of the world. These people find use in their English devices, because websites like YouTube provide content in their language even when the interface is not in their language.

Sometimes these people cannot switch the interface language of the operating system. For example٫ Windows Single Language edition forbids changing the language of the interface, and it is common in developing countries.