OptionSetValueから表示名を取得

//This method will return the label for the LCID of the account the IOrganizationService is using
public static string GetOptionSetValueLabel(string entityName, string fieldName, int optionSetValue, IOrganizationService service)
{
var attReq = new RetrieveAttributeRequest();
attReq.EntityLogicalName = entityName;
attReq.LogicalName = fieldName;
attReq.RetrieveAsIfPublished = true;

var attResponse = (RetrieveAttributeResponse)service.Execute(attReq);
var attMetadata = (EnumAttributeMetadata)attResponse.AttributeMetadata;

return attMetadata.OptionSet.Options.Where(x => x.Value == optionSetValue).FirstOrDefault().Label.UserLocalizedLabel.Label;

}

//This method will return the label for the specified LCID
public static string GetOptionSetValueLabel(string entityName, string fieldName, int optionSetValue, int lcid, IOrganizationService service)
{
var attReq = new RetrieveAttributeRequest();
attReq.EntityLogicalName = entityName;
attReq.LogicalName = fieldName;
attReq.RetrieveAsIfPublished = true;

var attResponse = (RetrieveAttributeResponse)service.Execute(attReq);
var attMetadata = (EnumAttributeMetadata)attResponse.AttributeMetadata;

return attMetadata.OptionSet.Options.Where(x => x.Value == optionSetValue).FirstOrDefault().Label.LocalizedLabels.Where(l => l.LanguageCode == lcid).FirstOrDefault().Label;

}