当页面重新加载自定义选择列表值刷新时

Question

长期以来，我一直需要您的帮助：

问题： 我创建了如下的自定义选择列表，当页面刷新时，选择列表的值也被刷新。我要保留它。请让我知道我在哪里做错了。

在此方面，任何帮助将不胜感激。谢谢

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    Visualforce Page:

    <apex:form >
    <apex:pageBlock >
      <apex:pageBlockSection >
        <apex:selectList value="{!SelectLanguage}" multiselect="false" size="1">                
            <apex:selectOptions value="{!LanguageOptions}" />
            <apex:actionSupport event="onchange" action="{!Refresh}"/>
            </apex:selectList>                
        </apex:pageBlockSection>    
        </apex:pageBlock>
    </apex:form>


Controller:
    //Controller to create and add picklist value

               public String SelectLanguage{get;set;}
               public String LanguageOption{get;set;}

               public List<SelectOption> getLanguageOptions() 
        {
            List<SelectOption> LanguageOption= new List<SelectOption>();
            LanguageOption.add(new SelectOption(',','Language'));
            LanguageOption.add(new SelectOption('Es_US','English'));
            LanguageOption.add(new SelectOption('Da','Danish'));
            LanguageOption.add(new SelectOption('nl_NL','Dutch'));
            LanguageOption.add(new SelectOption('zh_TW','Chinese (Traditional)'));
            return LanguageOption;
        }

 // Page refresh with additional language parameter   
        public pagereference Refresh() {
            string langcode = SelectLanguage;
            pagereference pg=new pagereference('/supportagent/supportAgentPage?lang=es_US');
            pg.getParameters().put('lang',SelectLanguage);
            pg.setRedirect(true);
            return pg;

        }