Hi,
What i understoond is that you have different pages for each langauge and you want to populte the menu control with the pages of the currently selected langauge , right?
You can create two SiteMapDatasources and set the Menu datasource for one of based on the lanague .
For Configuring multiple SiteMapDataSources , check :
http://msdn.microsoft.com/en-us/library/ms178426.aspx
After configuring the datasources , you can set the menu DataSourceId property in code behind based on the current language:
for example, in Page_Laod of the masterPage:
If( this.Page.UICulture=="en-US")
Menu1.DataSourceId="EnglishSiteDataSource";
else
Menu1.DataSourceId="OtherSiteDataSource";