Proposed Solution:
<HTML lang="<%= PageLanguage %>">
. , , . runat = "server" HTML, HtmlGenericControl Controls. , id, , :
<html runat="server" id="html">
codebehind:
html.Attributes["lang"] = "en";
: HTML- .
: , Aleris - "" (, LiteralControl) Controls, html ( doctype ..) ). , , ( ) - .