During the initial configuration or setup of the OnePlus smartphone, the region and the desired system language are already defined.

If we want to change the language afterwards, the device does not need to be reset to the factory settings.

To select a different language, simply drag the language to the first position of the existing languages, or first activate it using the Add a language button.

Android 10 | OxygenOS 10.0
Step 1:  Open the  Settings
Step 2:  Tap on  System
Step 3:  Tap on  Languages & input
Step 4:  Tap on  Languages (country/region)
Step 5:  Tap on  Add a language  or hold a  language
Step 6:  Drag the  language  to the first position
  1. Open the Settings
  2. Tap on System
  3. Tap on Languages & input
  4. Tap on Languages (country/region)
  5. Tap on Add a language or hold a language
  6. Drag the language to the first position

OnePlus Instructions