Sending a verification Email 

The purpose of verifying the email address is to avoid spam and invalid email addresses.  The following code shows how we can send a verification email address using the sendEmailVerification method:

FirebaseAuth auth = FirebaseAuth.getInstance();
FirebaseUser user = auth.getCurrentUser();

user.sendEmailVerification()
        .addOnCompleteListener(new OnCompleteListener<Void>() {
            @Override
            public void onComplete(@NonNull Task<Void> task) {
                if (task.isSuccessful()) {
                    Log.d(TAG, "Email sent.");
                }
            }
        });

We can customize the email templates as well; to customize the email templates you can visit Firebase help center. Also, we can change the language of the mail.