is wifi calling free on international calls?

Note that if you’re referring to your carrier‘s wifi calling feature, then regular minutes and rates apply, regardless of the wifi connection itself - Wi-Fi Calling from AT&T

Wifi calling from carriers merely routes your call over wifi instead of cellular in areas where cellular signal is weak or non-existent. But wifi calls are still calls on your plan.

VOIP (e.g FaceTime, Skype) calls may be free if the wifi and VOIP Service are free.

It is if you aren't paying for the WiFi connection.