Hi Steve and Gale,
Thanks for the questions…
The idea is not to have to press play, pause, play, pause, etc… the file should have the spaces so that you could for instance be playing it in a car as you drive along without being distracted - simply play it on loop and practice.
There is no need to repeat (duplicate) the actual spoken phrases within the file - just allow enough space for the listener to repeat the last phrase and then continue to the next phrase, and so on. The repetition comes with playing the file over and over. The person who uses this proposed plugin would decide how long the practice segments should be, as needed.
The actual silence should be real silence - no background noise or effect is needed because for instance in a car, or home, there is already enough noise - or at home, soft music could be playing somewhere in the house anyway. So, the file should be clean in that sense. I’m saying this because the spoken files I’m using are well recorded and very clean. But I take your point, if it was a dirty recording, then pure silence might sound weird… in that case, the quality of the recording (in my opinion) is probably not worth using anyway. I can’t stand listening to badly recorded stuff - vocal or otherwise 
I experimented with the length of silence and found 3 seconds to be a fair compromise if the length of silence must be a fixed length - but another way of doing it is to make the silence a variable length based on the length of the vocal phrase, multiplied by a comfort factor (CF) that could be set by slider control, say between x1 to x5. So, for instance, if the phrase was 3 seconds long, and the CF (for the whole file) was set to x2 - then the inserted silence would be 6 seconds i.e. 3 seconds x2. If the CF was set to x1.5 then it would of course create a 4.5 second gap.
Language translation and languages in general is a huge thing these days… Google and Microsoft are both into it big time. I find it hard to believe that this software (or plugin) doesn’t yet exist. I would be using it non-stop. All I can tell you is that the numbers of people who would use this (if they knew it was available) is vast and covers the whole world.
I really hope you can do it!
Thanks again!
John