Identify any changes in language on a page by using a correct value in the lang or xml:lang attribute, as appropriate for the HTML or XHTML version you use. HTML uses the lang attribute on elements. XHTML 1.0 allows both lang and xml:lang attributes, and XHTML 1.1 and above allows only xml:lang.
Engine scans elements for empty or invalid xml-lang attributes
Identifying changes in language is important for a number of reasons:
It allows braille translation software to follow changes in language.
Speech synthesizers that support multiple languages will be able to speak the text in the appropriate accent with proper pronunciation. If changes are not marked, the synthesizer will try its best to speak the words in the default language it works in. Thus, the French word for car, “voiture” would be pronounced “voyture” by a speech synthesizer that uses English as its default language.