Diacritics is a scripting type which is not supported by Google web fonts. Because of this, those letters will render as the fallback font and not in the font selected by the user. These characters may look like they’re bold, but in fact, that’s just the default style of Diacritics.
To solve this issue, please select a different font and see if the new font renders the diacritics in a better manner.
To learn more about this occurrence, please read this in-depth article.