You can change the language setting on your iPhone or iPad if it's incorrect or if you've accidentally changed the language to one you don't understand.
Use Markup to add text, shapes, signatures, and more to documents on iPad - Apple Support
Use tones and ringtones with your iPhone or iPad - Apple Support
Set up your iPhone or iPad - Apple Support
How to Change App Language on Your iPhone or Mac
Set up multiple calendars on iPad - Apple Support
Change Language on iPhone or iPad
Official Apple Support
Use Visual Look Up to identify objects in your photos and videos on iPhone – Apple Support (UK)
How to set up and use Personal Voice and Live Speech on iPhone and iPad
Add, edit, and remove widgets on iPhone - Apple Support
Use Quick Start to set up a child's iPhone or iPad - Apple Support
How to Change Language on APPLE App Store?