Write localized App Store metadata (description, keywords, promotional text, what's new, URLs) plus app name and subtitle via the App Store Connect API

Documented steps

1. Get the target appStoreVersion id (e.g. via GET /v1/apps/{id}/appStoreVersions), then list its localizations: GET /v1/appStoreVersions/{id}/appStoreVersionLocalizations?fields[appStoreVersionLocalizations]=description,locale,keywords,marketingUrl,promotionalText,supportUrl,whatsNew
2. If a localization for your locale exists, keep its id and go to the PATCH step; otherwise create one.
3. Create: POST /v1/appStoreVersionLocalizations with body {"data":{"type":"appStoreVersionLocalizations","attributes":{"locale":"en-US","description":"...","keywords":"...","marketingUrl":"https://...","promotionalText":"...","supportUrl":"https://...","whatsNew":"..."},"relationships":{"appStoreVersion":{"data":{"type":"appStoreVersions","id":"<versionId>"}}}}}
4. locale must be an App Store Connect locale shortcode (en-US, es-ES, fr-CA, zh-Hans, pt-BR, ja, ...) and is required on create.
5. curl: curl -X POST https://api.appstoreconnect.apple.com/v1/appStoreVersionLocalizations -H "Authorization: Bearer $JWT" -H "Content-Type: application/json" -d '{"data":{"type":"appStoreVersionLocalizations","attributes":{"locale":"en-US","whatsNew":"Bug fixes"},"relationships":{"appStoreVersion":{"data":{"type":"appStoreVersions","id":"123"}}}}}'
6. Update: PATCH /v1/appStoreVersionLocalizations/{id} with {"data":{"type":"appStoreVersionLocalizations","id":"<id>","attributes":{ ...only changed fields... }}}. Omitted attributes are left untouched.
7. promotionalText can be PATCHed at ANY time, including while the version is live — it needs no new build and does not trigger review.
8. description, keywords, marketingUrl, supportUrl and whatsNew can only be changed while the version is in an editable state. Check first: GET /v1/appStoreVersions/{id}?fields[appStoreVersions]=appVersionState
9. App name and subtitle are NOT on appStoreVersionLocalizations. They live on appInfoLocalizations, which hangs off the app-level appInfos resource.
10. Get the appInfo id: GET /v1/apps/{id}/appInfos, then list GET /v1/appInfos/{id}/appInfoLocalizations
11. Create app-level localization: POST /v1/appInfoLocalizations with {"data":{"type":"appInfoLocalizations","attributes":{"locale":"en-US","name":"...","subtitle":"...","privacyPolicyUrl":"https://...","privacyPolicyText":"..."},"relationships":{"appInfo":{"data":{"type":"appInfos","id":"<appInfoId>"}}}}}
12. Update with PATCH /v1/appInfoLocalizations/{id}; editability is governed by appInfos.attributes.state.
13. Remove a localization with DELETE /v1/appStoreVersionLocalizations/{id} or DELETE /v1/appInfoLocalizations/{id}.
14. Official docs: https://developer.apple.com/documentation/appstoreconnectapi/app-store-version-localizations | https://developer.apple.com/documentation/appstoreconnectapi/app-info-localizations | https://developer.apple.com/documentation/appstoreconnectapi/managing-metadata-in-your-app-by-using-locale-shortcodes