Identifers for text and flashbacks
My wife and I have watched your dramas every night for years and are wholly dependent upon English subtitles.
Two things occur in every episode of every drama and are easily misunderstood: (1) subtitle text when the actor is thinking to himself rather than speaker out loud, and (2) flashback footage. Both of these should have some kind of visual marker identifying them for the viewer.
The simple marker for the subtitle text of actor's thought is to write it in italics.
Marking flashbacks might be done by a different color cast for the flashback -- black & white, or a yellowish cast -- or even the words "flashiback" in the upper left corner of the screen.
Your video technicians are more adept than me at finding a workable marker for marking footage so that the viewer knows he is seeing a flashback, and I ask them to do so.
State of Washington, USA.