I have two of the first gen X1 boxes, the ones with the clock display on the front panel.
My boxes are showing the same kind of dialog skipping, and it's not just on foreign films. It's on all shows -- foreign and domestic, movies and TV shows.
This started happening several months ago, I don't remember the exact date.
The wife still puts up with it, but I've switched to watching Netflix through our Roku devices, which do not have this dialog problem.
Comcast (xFinity) advised to send an Email to: firstname.lastname@example.org
providing detailed information on the movie that you experienced difficulty with. Specific info regarding Day, Date, Hour/Minute Location in the movie, etc.
i did not think it would be worth it to try and go back to the novie and find all the details.
when you select a title (not episode) the menu is available on left side to change audio and subtitles. are you not seeing that menu? for example on Sabrina it offers English (CC)
The problem I initially posted was not about being able to turn closed captioning on and off.
The problem was related to closed captioning not following the on screen action. Also at times the closed captioning would be missing at times.
you can determine issue of sync if delayed by pausing the audio and watching to see if the captions continue printing on the screen 'catching up'. if this happens, the decoding device is the problem (in this case set top box). only broadcast items and new usa productions have a requirement for subtitles. Live translations are controlled by the producer of the program (like local evening news programs). if there are no subtitles/captions. you can test an issue of missing caption diagnosis by using a parallel different device like a smart phone/tablet playing the same title.