My browser is in English and I have removed all other languages, but when I go to the console and look up navigator.language it shows a value of "bg-BG" and navigator.languages is ["bg-BG", "en"].
I tried normal and hard reloads of the page, restarting Chrome, clearing the browsing data, even restoring the settings to their original defaults. Then I decided that if not removing it I can maybe move it lower if I add Bulgarian as a language and move that lower and now navigator.languages is equal to ["bg-BG", "en", "bg"].
If I add a new person to Chrome they don't have "bg-BG" in their navigator.languages and their default is English.
edit: I found a way that temporarily fixes it. If I select a language and pick Move to the top it will go above bg-BG, but newly added languages will still go under it. So it's still in the list in the languages settings, just hidden and unselectable.
chrome://settings/?search=lang).