The :lang pseudo-class sets the language for a tag. For example:
p:lang(en) {text-align: left;}
You might use this to set up quotation marks for a document that is in French or German.
More information
Pseudo classes and elements
a:link, a:active and a:visited
a:hover
:cursor
first-child
first-line
first-letter
focus
lang
@import
!important
