Add language_override field to Contacts API in Unstable version (#343)

Add support for the language_override field in the Contacts API
for both create and update endpoints in the Unstable version.

Changes:
- Add language_override to create_contact_request schema
- Add language_override to update_contact_request schema
- Update language_override description in contact response schema

The language_override field:
- Is a preferred language setting for contacts
- Used by Intercom for Fin and Messenger language
- Supports ISO 639-1 two-letter language codes
- Invalid codes are set to null
- Available only in Unstable API version

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: colinfkennedy

descriptions/0/api.intercom.io.yaml

@@ -16994,8 +16994,10 @@ components:
         language_override:
           type: string
           nullable: true
-          description: A preferred language setting for the contact, used by the Intercom
-            Messenger even if their browser settings change.
+          description: A preferred language setting for the contact, used by Intercom
+            as the language of Fin and the Messenger even if their browser has a different
+            setting. Supports ISO 639-1 two-letter language codes. If an unsupported
+            code is supplied, the field will be set to null.
           example: en
         browser:
           type: string
@@ -18559,6 +18561,14 @@ components:
           nullable: true
           description: Whether the contact is unsubscribed from emails
           example: true
+        language_override:
+          type: string
+          nullable: true
+          description: A preferred language setting for the contact, used by Intercom
+            as the language of Fin and the Messenger even if their browser has a different
+            setting. Supports ISO 639-1 two-letter language codes. If an unsupported
+            code is supplied, the field will be set to null.
+          example: en
         custom_attributes:
           type: object
           nullable: true
@@ -23014,6 +23024,14 @@ components:
           nullable: true
           description: Whether the contact is unsubscribed from emails
           example: true
+        language_override:
+          type: string
+          nullable: true
+          description: A preferred language setting for the contact, used by Intercom
+            as the language of Fin and the Messenger even if their browser has a different
+            setting. Supports ISO 639-1 two-letter language codes. If an unsupported
+            code is supplied, the field will be set to null.
+          example: en
         custom_attributes:
           type: object
           nullable: true