add instructions for other intl contributors

CONTRIBUTING.md

@@ -14,4 +14,82 @@ Please conform to [standard](https://standardjs.com/) for code styles.
 ## Submitting Pull Request
 Please follow GitHub's standard model of making changes & submitting pull request which is very well explained [here](https://guides.github.com/activities/forking/). Make sure your code works fine locally before submitting a pull request.
 
+## Internationalization
+Remix is now support Internationalization. Everyone is very welcome to contribute on this feature.
 
+### How to make a string support intl?
+First, put the string in the locale file located under `apps/remix-ide/src/app/tabs/locales/en`.
+Each json file is corresponding to a module. If the module not exist, create a new json and import it in the `index.js`.
+Then you can replace the string with a intl component. The `id` prop will be the key of this string.
+```jsx
+<label className="py-2 align-self-center m-0" style={{fontSize: "1.2rem"}}>
+-  Learn
++  <FormattedMessage id="home.learn" />
+</label>
+```
+In some cases, jsx maybe not acceptable, you can use `intl.formatMessage` .
+```jsx
+<input
+   ref={searchInputRef}
+   type="text"
+   className="border form-control border-right-0"
+   id="searchInput"
+-  placeholder="Search Documentation"
++  placeholder={intl.formatMessage({ id: "home.searchDocumentation" })}
+   data-id="terminalInputSearch"
+/>
+```
+
+### How to add another language support?
+Let's say you want French.
+
+First, create a folder named by the language code which is `fr`.
+Then, create a json file, let's say `panel.json`,
+```json
+{
+  "panel.author": "Auteur",
+  "panel.maintainedBy": "Entretenu par",
+  "panel.documentation": "Documentation",
+  "panel.description": "La description"
+}
+```
+Then, create a `index.js` file like this,
+```js
+import panelJson from './panel.json';
+import enJson from '../en';
+
+// There may have some un-translated content. Always fill in the gaps with EN JSON.
+// No need for a defaultMessage prop when render a FormattedMessage component.
+export default Object.assign({}, enJson, {
+  ...panelJson,
+})
+```
+Then, import `index.js` in `apps/remix-ide/src/app/tabs/locale-module.js`
+```js
+import enJson from './locales/en'
+import zhJson from './locales/zh'
++import frJson from './locales/fr'
+
+const locales = [
+  { code: 'en', name: 'English', localeName: 'English', messages: enJson },
+  { code: 'zh', name: 'Chinese Simplified', localeName: '简体中文', messages: zhJson },
++  { code: 'fr', name: 'French', localeName: 'Français', messages: frJson },
+]
+```
+You can find the language's `code, name, localeName` in this link
+https://github.com/ethereum/ethereum-org-website/blob/dev/i18n/config.json
+
+### Whether or not to use `defaultMessage`?
+If you search `FormattedMessage` or `intl.formatMessage` in this project, you will notice that most of them only have a `id` prop, but a few of them have a `defaultMessage` prop.
+
+**Why?**
+
+Each non-english language will be filled in the gaps with english. Even there maybe some un-translated content, it will always use english as defaultMessage. That why we don't need to provide a `defaultMessage` prop each time we render a `FormattedMessage` component.
+
+But in some cases, the `id` prop may not be static. For example,
+```jsx
+<h6 className="pt-0 mb-1" data-id='sidePanelSwapitTitle'>
+ <FormattedMessage id={plugin?.profile.name + '.displayName'} defaultMessage={plugin?.profile.displayName || plugin?.profile.name} />
+</h6>
+```
+You can't be sure there is a match key in locale file or not. So it will be better to provide a `defaultMessage` prop.