Apples iOS 13 makes the iPhone and iPad multilingual. Now you can change the language of an individual application without change the main language of your system. Each application can have its own language setting.
First, make sure your iPhone or iPad has multiple languages installed. To do this, go to Settings> General> Language and Region. Tap on "Other Languages" and add the language you want to use.
It is also here that you can set the overall system language on your iPhone or iPad. But you do not have to switch to the new language, add it to this list.
Then go to the main Settings screen and scroll to the alphabetical list of installed applications. Tap the application for which you want to change the language settings.
You will see a "Language" option under Preferred Language. Tap and select the language you want to use for this application.
Repeat this procedure to change the language individually for additional applications.
Not all applications offer multiple languages. If an application does not offer additional languages, you will not see any language options on its settings screen.
If you do not see the Language option on the application setup screen, multiple languages are probably not installed on your device.
Go to Settings> General> Language and Region and make sure you have more than one language on the list. Otherwise, the Language by Application option will not appear.