Open WhatsApp
Open any chat
Tap the message box
Switch your keyboard to Marathi
If Marathi is not available, add a Marathi keyboard in your phone settings
On Android, go to Settings > System > Languages & input > On-screen keyboard > Gboard > Languages > Add keyboard > Marathi
On iPhone, go to Settings > General > Keyboard > Keyboards > Add New Keyboard > Marathi
Type using the Marathi keyboard
Send the message
If needed, use transliteration by typing Marathi words in English and selecting Marathi suggestions on the keyboard