You can check for Serbian subtitles by going to Account > Profiles > Languages and adding Serbian to your preferred list.

If you have the movie file on your computer, you can manually add a Serbian .srt file:

Finding for The Mummy franchise involves navigating both dedicated subtitle libraries and streaming settings. Whether you're watching the 1999 classic or the 2017 reboot, here is how you can find and apply them. Where to Find Serbian Subtitles