MeGUI has a tool called VobSubber.
It can extract .idx/.sub from a .vob.
I have many DVDs contain multiple languages subtitles.
The default language of them is Chinese.
Thus, after extract .idx/.sub, "langidx" in .idx is 0 (select the Chinese).
Could VobSubber provide an option for setting langidx in .idx to another value after extracting .idx/.sub?
Otherwise, we have to manually modify .idx by text editor.