feat: add readme for i18n

packages/i18n/README.md

@@ -0,0 +1,62 @@
+# i18n
+
+## Usages
+
+- Update missing translations into the base resources, a.k.a the `src/resources/en.json`
+- Replace literal text with translation keys
+
+```tsx
+import { useTranslation } from '@affine/i18n';
+
+// src/resources/en.json
+// {
+//     'Text': 'some text',
+//     'Switch to language': 'Switch to {{language}}', // <- you can interpolation by curly brackets
+// };
+
+const App = () => {
+  const { t } = useTranslation();
+
+  const changeLanguage = (language: string) => {
+    i18n.changeLanguage(language);
+  };
+
+  return (
+    <div>
+      <div>{t('Text')}</div>
+
+      <button onClick={() => changeLanguage('en')}>
+        {t('Switch to language', { language: 'en' })}
+      </button>
+      <button onClick={() => changeLanguage('zh-Hans')}>
+        {t('Switch to language', { language: 'zh-Hans' })}
+      </button>
+    </div>
+  );
+};
+```
+
+## How the i18n workflow works?
+
+- When the `src/resources/en.json`(base language) updated and merged to the develop branch, will trigger the `languages-sync` action.
+- The `languages-sync` action will check the base language and add missing translations to the Tolgee platform.
+- This way, partners from the community can update the translations.
+- Finally, the `languages-download` action will regularly download the latest translation resources from the Tolgee platform.
+
+## How to sync translations manually
+
+- Set token as environment variable
+
+```shell
+export TOLGEE_API_KEY=tgpak_XXXXXXX
+```
+
+- Run the `sync-languages:check` to check all languages
+- Run the `sync-languages` script to add new keys to the tolgee platform
+
+## References
+
+- [AFFiNE | Tolgee](https://i18n.affine.pro/)
+- [Tolgee Documentation](https://tolgee.io/docs/)
+- [i18next](https://www.i18next.com/)
+- [react-i18next](https://react.i18next.com/)