The additional language subtitles you see in the background of videos are hardsubs, i.e. they are burned into the video itself, provided by our content provider, and there is no way to turn them off.
If the subtitles overlap each other, you can add a background color/opacity to the subtitles added to this show (on top of the hardsubs) by managing your subtitles appearance settings. Learn how you can do that on the various devices:
Viki app on your iOS device: How do I change subtitle size, font & color on iOS?
Viki app on your Android device: How do I change subtitle settings on Android app?
On a web browser at Viki.com: How do I change subtitle appearance on the Viki web player?
On your Roku device: Roku - How can I change the subtitle language, size and style?
You can turn off the background color/opacity of subtitles for other shows if you no longer need them.