Okay, testing done. Luckily, the biggest issue was me being careless (opening KotOR journal file while program was in TSL mode) but, considering how easy that kind of thing is... though the quest names not showing if there's wrong dialog.tlk file in use is not surprising, one would expect that swapping the program to another mode (TSL->KotOR) would refresh the quest list. It does not, you must reopen the journal file, and that is pretty confusing. Suggestion: make the quest list to refresh (or force-reopen the journal file without user needing to do so) if there is a journal file open when toggling the mode.
Plus, there seems to be some error handling missing. If you accidentally open a journal file with wrong dialog.tlk (if you open TSL journal in KotOR mode, or if you have original dialog.tlk in game folder and you are trying to open modded journal file with additional strrefs in it) program crashes, because it tries to read a string after the end of dialog.tlk. Suggestion: add try-catch block - or whatever it is called in Perl - or some kind of error handling anyway, to catch that error and handle it correctly. Users don't like programs crashing.
What's with me, can't type anymore - wrote "dalek.tlk" in here.
But good news last: these problems don't appear, if it is used correctly. So if you don't constantly jump from one game to another, you should be fine.