ColorOS is a slightly modified Android and therefore the Oppo-Smartphone offers all languages that are available on normal Android devices.

Android 10 | ColorOS 7.0
Step 1:  Open the  Settings
Step 2:  Tap on  Language & region
Step 3:  Tap on  Language
Step 4:  Choose desired  Language
Step 5:  Tap on  Done
Step 6:  Confirm with  Change to xxxxxx
  1. Open the Settings
  2. Tap on Language & region
  3. Tap on Language
  4. Choose desired Language
  5. Tap on Done
  6. Confirm with Change to xxxxxx

Oppo Instructions