Base Document Language
It’s a good practice to declare the primary language of the document in the html element:
If no other lang attribute is specified in the document, it means that everything (i.e., element content and attribute
text values) is in that language.
If the document contains parts in other languages, these parts should get their own lang attributes to “overwrite”
the language declaration.
The lang attribute is used to specify the language of element content and attribute text values:
<p lang="en">The content of this element is in English.</p> <p lang="en" title="The value of this attribute is also in English.">The content of this element is in English.</p>
The language declaration gets inherited:
<div lang="en"> <p>This element contains English content.</p> <p title="This attribute, too.">Same with this element.</p> </div>
Elements with Multiple Languages
You can “overwrite” a language declaration:
<p lang="en">This English sentence contains the German word <span lang="de">Hallo</span>.</p>
It is possible to add the attribute hreflang to the elements <a> and <area> that create hyperlinks. Such it specifies
the language of the linked resource. The language defined must be a valid BCP 47 language tag.
<p> <a href="example.org" hreflang="en">example.org</a> is one of IANA's example domains. </p>
- ↑ IETF Network Working Group: RFC 5646 Tags for Identifying Languages, IETF, September 2009
Handling Attributes with Different Languages
You can “overwrite” a parent element’s language declaration by introducing any element apart from applet, base,
basefont, br, frame, frameset, hr, iframe, meta, param, script (of HTML 4.0) with an own lang attribute:
<p lang="en" title="An English paragraph"> <span lang="de" title="A German sentence">Hallo Welt!</span> </p>