Web Reader doesn't automatically detect English pages

I’m using the Web Reader to import texts, and it usually detects the page language correctly, except when the text is in English.

For example, if I import an article from a Spanish newspaper, it automatically displays the message, “This page looks like Spanish,” along with a “Switch to Spanish” button.

However, when I import an article from a British newspaper, no language detection message is shown, and I have to switch the language to English manually.