For those interrested the problem was a minor one.
In DirectVobSub configuration, Misc tab, "Pre-Buffer subpicture" must remain unchecked or it will mess with subtitles animation.
Now the Queen's blade subtitles animation works with kanji and romaji, the mixed kanji/romaji lines work in railgun 14 OP (around 2'50"), ladies versus buttler op with animated subs all around screen works.
I have yet to find a non hardcoded very rich animated subtitle: with littles stars/hearts and complex animation as we get in some ops. But it's of a very little importance now that I cover like 99% of subtitles needs.