Thanks for the answer. Hope there could be something done eventually, but I understand.I don't have a good solution for this slowdown because every time there is a "new" text to display, the tool needs to handle the text display.
This process will often even catch text that will not be displayed, as long as the game deals with these things in some way, the tool will stepping in.
And then the bigger the game texts are, the more slower it gets.
It is involved in the display process unlike other tools which simply send the text out, it receives it, processes it and returns it to the game, during this period the game is stalled.
There is a lot of text processing going on, and I've optimized the performance as much as possible, which is the best I can do.
There may be better changes in the future, but I won't be working on it specifically for now.
Because the result may not be better in all cases, it may be worse.
That said, it is weird how it almost works correctly/much better when switching back to the JP text (but mtool is doing the rendering/displaying still).