Open WhatsApp
Tap the text field to open the keyboard
Tap the globe icon, language key, or spacebar and swipe if your keyboard supports it
If needed, open your phone settings
Go to Keyboard settings
Add or enable the desired language
Return to WhatsApp and switch to the new keyboard language
On iPhone, go to Settings > General > Keyboard > Keyboards > Add New Keyboard
On Android, go to Settings > System > Languages & input > On-screen keyboard > your keyboard app > Languages
If using Gboard, open Gboard settings and add the language there
If using Samsung Keyboard, open Samsung Keyboard settings and add the language there