The language set defaults to the language set in the OS, which is usually the preferred language for most users.
You have people working in IT who set their language to English for easier troubleshooting (i.e. not needing to Google error codes), but they're a small minority.
Anyone handling more than one language daily will be doing an explicit choice, and I wouldn't say they're a minority.
If your native tongue is Spanish but you live in the US for instance, the "preferred" language in your browser has IMHO a higher chance of being English. Same if you live in India probably.
