MultiLangString mlsTestValue = new MultiLangString();
mlsTestValue.AddString(ISOCode.Language.L_de_DE, "Test043c");
string strPropertyIdentyfingName = "Page.Test043c";
UserDefinedPropertyDefinition oUDPD = UserDefinedPropertyDefinition.Create(m_oProject, strPropertyIdentyfingName, UserDefinedPropertyDefinition.Enums.ClientType.Page);

//set test property
Page oPage = m_oProject.Pages[0];
oPage.Properties[strPropertyIdentyfingName] = mlsTestValue;

//search page with property value
DMObjectsFinder oFinder = new DMObjectsFinder(m_oProject);
PagesFilter oPagesFilter = new PagesFilter();
PagePropertyList oPagePropertyList = new PagePropertyList();
AnyPropertyId oAnyPropertyId = new AnyPropertyId(m_oProject, strPropertyIdentyfingName);
oPagePropertyList[oAnyPropertyId] = mlsTestValue;
oPagesFilter.SetFilteredPropertyList(oPagePropertyList);
Page[] arrPages1 = oFinder.GetPages(oPagesFilter);