Sometimes is useful to set a cookie with javascript. You can use the function below.

function Set_Cookie(name, value, expires, path, domain, secure )
{
var today = new Date();
today.setTime( today.getTime() );

if ( expires ) { expires = expires * 1000 * 60 * 60 * 24; }
var expires_date = new Date( today.getTime() + (expires) );
document.cookie = name + "=" +escape( value ) + ( ( expires ) ? ";
expires=" + expires_date.toGMTString() : "" ) + ( ( path ) ? ";path=" + path : "" ) + ( ( domain ) ? ";domain=" + domain : "" ) + ( ( secure ) ? ";secure" : "" );

}

Use it this way:
Set_Cookie(“language”, “fr”);