The app is not available in the mainland China store. The App Store storefront is determined by the country or region of the Apple ID used under Media & Purchases, not by the device's current language. Your physical location alone does not determine the storefront either. If you cannot find the app, check your account region first, then open the product page on this site. Do not choose an app based only on a similar name in search results.
Check the following path: Settings → Apple ID → Media & Purchases → View Account → Country/Region. The system may ask you to verify your account first. Check the country or region shown there and confirm that it matches the storefront you expect to use. The account menu layout may vary slightly between system versions; follow the labels shown on your device.
If you need to change your region, the Country/Region page provides the option. Whether the change can be completed depends on your account balance, existing subscriptions, Family Sharing status, and the requirements of the destination region. Review system prompts and resolve any conditions first; a region change cannot be assumed to take effect immediately. This section explains the account settings path only.
This store information does not apply to computers or Android devices: use the corresponding installer on this page for Mac, Windows, Android, and Linux. iPhone / iPad costs $2.99 once in the App Store; the other four platforms are free. These are two separate ways to get the app.