Theme switch support (#3568)

### What problem does this PR solve?
- [x] New Feature (non-breaking change which adds functionality)

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Co-authored-by: Yingfeng <yingfeng.zhang@gmail.com>
Co-authored-by: Jin Hai <haijin.chn@gmail.com>

web/src/pages/add-knowledge/components/knowledge-setting/configuration.tsx

@@ -70,6 +70,7 @@ const ConfigurationForm = ({ form }: { form: FormInstance }) => {
         <Select placeholder={t('languagePlaceholder')}>
           <Option value="English">{t('english')}</Option>
           <Option value="Chinese">{t('chinese')}</Option>
+          <Option value="Vietnamese">{t('vietnamese')}</Option>
         </Select>
       </Form.Item>
       <Form.Item