It sounds like you want to read subs and translate titles on the fly on live tv,is not?
I tell you one thing that might seem simple to you,but is a big problem to do : synchronize live stream with a file you have to read and then overlay on screen.
A stream is never perfect,so handling hicups is a mess,even more so when signal strength is low.
Then comes the part where the only thing you could use the sync is the PCR (program clock reference) that does not have any relation to the video showing,is the reference between parts the player obey to play audio and video at the same time,and is not related to the content,doesn't care what the content is,this PCR does not point to an specific audio event you need to sync to in order to show the sub for that part,but it just say this audio mark align with this video mark,that is all.
It does not say "this is the minute 34 of the movie" which you would need to sync the sub to it.
As a relation,subs in stream are easy to align,since they use the same PCR as video and audio,so playing them together in sync is possible.
You cannot simply sync an external file with a live stream.
And this is only the first problem I can see.
There are tons more.