If the filename format will stay same you could do this
string cultureCode = "en-US"; //set current locale
Uri reportUri = new Uri(String.Format("http://www.xyz.com/report/report.{0}.htm", cultureCode), UriKind.Absolute);
That way it'll dynamically create the URI for you with the relevant locale added. As a quick method
public void Uri GetLocalReportUri(string cultureCode)
{
return new Uri(String.Format("http://www.xyz.com/report/report.{0}.htm", cultureCode), UriKind.Absolute);
}