revision:
The attribute contains a single “language tag” in the format defined in Tags for Identifying Languages (BCP47). The lang attribute is a global attribute, and can be used on any HTML element.
The default value of lang is unknown, therefore it is recommended to always specify this attribute with the appropriate value. Usage of lang attribute helps the browser to display the text in the desired language.
<element lang="language-code "></element>
If the attribute value is the empty string (lang=""), the language is set to unknown; if the language tag is not valid according to BCP47, it is set to invalid. To ensure your page's content is pronounced correctly for screen reader users, use a valid language code in the lang attribute of the <html> element. E.g. <html lang="en">
Ceci est un paragraphe.
This paragraph is English, but the language is not specifically defined.
This paragraph is defined as British English.
<p class="spec" lang="fr">Ceci est un paragraphe.</p>
<p class="spec">This paragraph is English, but the language is not specifically defined.</p>
<p class="spec" lang="en-GB">This paragraph is defined as British English.</p>
<h4>I am a heading - <span lang="de-DE">Eine Überschrift</span></h4>