add i18n doc for custom layout

docs/get_started/en/usage/i18n.md

@@ -126,6 +126,24 @@ Then
     }
 ```
 
+## Layout template internationalization
+
+Use [custom layout](./layout_template.md), if you want to internationalize, you can use `{{gettext}}` for internationalization, for example:
+
+```html
+{{gettext("Hello world")}}
+```
+or
+```html
+{{_("Hello world")}}
+```
+
+Execute `teedoc build` or `teedoc serve` will automatically generate translation files in the `layout/locales` directory, and manually edit the `po` file in `layout/locales/`.
+> It will automatically generate two files `layout/i18n_babel.cfg` and `layout/i18n_locales.cfg`. The former is to set the scanned file, and the latter is to set the language to be translated. Modify it according to the situation.
+
+
+> Except for using the gettext method of Jinja2 template for translation, you can also use the method of web front-end for translation, please refer to relevant information by yourself.
+
 
 ## Plug-in internationalization
 

docs/get_started/zh/usage/i18n.md

@@ -125,6 +125,25 @@ pybabel --list-locales
     }
 ```
 
+## 布局模板国际化
+
+使用[自定义布局](./layout_template.md)时，如果想要国际化，可以使用`{{gettext}}`来进行国际化，比如：
+
+```html
+{{gettext("Hello world")}}
+```
+或者
+```html
+{{_("Hello world")}}
+```
+
+执行`teedoc build`或者`teedoc serve`时会在`layout/locales`目录下自动生成翻译文件，手动编辑`layout/locales/`下的`po`文件即可。
+也可以手动执行 `teedoc translate` 来更新翻译文件。
+> 会自动生成`layout/i18n_babel.cfg` 和 `layout/i18n_locales.cfg`两个文件，前者是设置扫描的文件，后者是设置需要翻译的语言，根据情况修改即可
+
+> 除了使用 Jinja2 模板的 gettext 方法来翻译，你也可以用网页前端的方法来翻译，请自行查阅相关资料。
+
+
 
 ## 插件国际化