<html>element's lang attribute tells it which language it is written in.
<html lang="en"> <!-- language set to English -->
That is, if
<html lang="en">is present but the text is actually in French, you'd hear a voice profile called Jack doing a bad impression of French, rather than a French profile called Jaques using authentic French pronunciation. It is possible to switch languages within a page using the lang attribute on child elements within the<body>.
For instance, I may want to quote some French within an English language page:
<blockquote lang="fr" > <p >Ceci n'est pas une pipe</p > <p >— <cite >René Magritte</cite > </p > </blockquote >
From Form Design Patterns