My point here is that this is a rather complex area that is very involved. If you want to even start broaching it I would strongly recommend getting used to Discourse first by itching other, smaller itches you have, that do not require major rearchitecture. I am not trying to solicit FREE help here, just trying to make sure you are set up for success.
This is a terrible idea for a first project with Discourse, its complicated, very complicated.
Also, I strongly recommend using the tool first as is and seeing if the current features work for you before trying to mold it into something it is not.
For your particular case I would strongly recommend focusing on getting RTL working as perfectly as a possible and perfecting the translation, both are far more important than another topic sorting.