No, actually if there are any missing exotic characters in the current font the browser will replace them with the same characters from another font that has them. You can even see which font is used in the browser’s Inspector. Those are the instances that I’d like to be able to highlight.
Many Google Fonts do not have glyphs for accented characters. They fall back to some standard font and you often have to look really closely to see whether “é” with an accent looks out of place compared to the “e” without an accent.