Zend下拉菜单标题不会被翻译

Question

我有一个野外县：

    $county = new Select('county');
    $county->setAttribute('id', 'county');
    $county->setAttribute('class', 'stored');
    $county->setAttribute('title', _('web.form.selfService.register.county.title'));
    $county->setAttribute('required', 'required');
    $county->setEmptyOption(_('web.form.selfService.register.county.emptyOption'));
    $county->setValueOptions($this->getDomainValues(Domain::COUNTY));
    $county->setLabel(_('web.form.selfService.register.county.label'));
    $this->add($county);

当县字段为空并且提交表单时，输出是源文本： web.form.selfService.register.county.title

此外，我在表单中有很多文本字段，其标题被翻译得很好。
示例：

    $firstName = new Text('firstName');
    $firstName->setAttribute('id', 'firstName');
    $firstName->setAttribute('class', 'stored');
    $firstName->setAttribute('placeholder', _('web.form.selfService.register.firstName.placeholder'));
    $firstName->setAttribute('title', _('web.form.selfService.register.firstName.title'));
    $firstName->setAttribute('required', 'required');
    $firstName->setLabel(_('web.form.selfService.register.firstName.label'));
    $this->add($firstName);

当第一个名字段留空并且表格被提交时，输出将是：
请插入名字