I understand that you want to know how to disable the subtitles when using the SlingCatcher.
The SlingCatcher features does not include the subtitles or the "Closed Caption" feature. This means that the subtitles are a feature that belongs to the AV source.
With this in mind, I encourage you to check the AV source settings in order to know how to adjust the subtitles. This way, you will be able to disable them.
Hope this helps!