The :lang() pseudo class selector in CSS matches elements based on the context of their given language attribute. Language in HTML, is determined by a combination of the lang="" attribute, the <meta> element, and by information from the protocol such as the HTTP Accept-Language request-header1 field. Acceptable language-code strings are specified in the HTML 4.0 specification.
The :lang() CSS pseudo-class matches elements based on the language they are determined to be in.
CSS lang selector select all matches element whose have lang attribute value "fr" (without single/double quote).
The :lang() selector is used to select elements with a lang attribute with the specified value.