Simply Learn app defines the native language in the app by the device's language. It means that if your phone is in Korean, when you open Simply Learn app to learn Thai, the translation for Thai words & sentences will be in Korean.
If you wish to change the native language in Simply Learn app, please follow these steps:
iOS device: Change the language in your device
1. Open the Language Picker by tapping on the flag on the top of the Home screen.
2. Change the language in "native language" section