docs: add i18n support to Logto email service (#1316)

Author: charIeszhao

docs/connectors/email-connectors/built-in-email-service.mdx

@@ -73,6 +73,27 @@ If no custom brand information is provided, the email template can still be used
   alt="Logto built-in email service sample without branding"
 />
 
+### Localization \{#localization}
+
+Logto's built-in email service supports multiple languages. It automatically detects the user's Sign-in Experience settings and sends emails in the user's preferred language.
+
+When sending organization invitations through Management API, you can specify the `locale` parameter in the request payload. E.g.:
+
+```json
+{
+  "inviterId": "inviter-user-id",
+  "invitee": "invitee-email-address",
+  "expiresAt": "epoch-timestamp",
+  "organizationId": "organization-id",
+  "messagePayload": {
+    "link": "https://your-app.com/invite-accept?invitation-id=abcd1234",
+    // highlight-start
+    "locale": "fr"
+    // highlight-end
+  }
+}
+```
+
 ## FAQs \{#faqs}
 
 <details>

docs/connectors/email-connectors/email-templates.mdx

@@ -42,7 +42,7 @@ Logto offers three distinct approaches for email template management:
      - [Logto Built-in Email Service](/connectors/email-connectors/built-in-email-service)
    - **Capabilities**:
      - ✅ Native variable support
-     - ❌ Multi-language templates _(Coming soon)_
+     - ✅ Multi-language templates
      - ❌ Template/UI modifications disabled
 
 ## Email template types \{#email-template-types}