System.Xml.Xsl.Runtime.XsltLibrary.LangToNameInternal C# (CSharp) Method

        internal static string LangToNameInternal(string lang, bool forwardCompatibility, IErrorHelper errorHelper)
        {
            string cultName = InvariantCultureName;

            if (lang != null)
            {
                // The value of the 'lang' attribute must be a non-empty nmtoken
                if (lang.Length == 0)
                {
                    if (!forwardCompatibility)
                    {
                        if (errorHelper != null)
                        {
                            errorHelper.ReportError(/*[XT_032]*/SR.Xslt_InvalidAttrValue, nameof(lang), lang);
                        }
                        else
                        {
                            throw new XslTransformException(SR.Xslt_InvalidAttrValue, nameof(lang), lang);
                        }
                    }
                }
                else
                {
                    // Check if lang is a supported culture name
                    try
                    {
                        cultName = new CultureInfo(lang).Name;
                    }
                    catch (System.ArgumentException)
                    {
                        if (!forwardCompatibility)
                        {
                            if (errorHelper != null)
                            {
                                errorHelper.ReportError(/*[XT_033]*/SR.Xslt_InvalidLanguage, lang);
                            }
                            else
                            {
                                throw new XslTransformException(SR.Xslt_InvalidLanguage, lang);
                            }
                        }
                    }
                }
            }
            return cultName;
        }