From what I understand, the version provided for purchase here does not have a 1:1 in Japanese on PC - the "remake" available in Japan is essentially the original JPN PC version just compatible for new operating systems. I could be wrong about this though.

Note: Falcom did develop the game, but in this case, XSEED has made modifications from the original JPN PC game so that all the PSP features are in their PC release. In this case, the localizer/publisher has added more features to this game than the original version did.

So how does the error manifest itself? Just an error message and missing sound, or are there crashes? I've already applied the Japanese voice patch. I can revert the game back to English voices, but I'd rather not do so if the error is just a minor nuisance.

Well, that's a new one. This must be the first time for that. Too bad about the original japanese version though :(

For more on the stuff they did for this ENG PC release, check this out:
http://xseedgames.tumblr.com/post/92769039590/xseed-blog-the-legend-of-heroes-trails-in-the-sky

Looks like above and beyond getting the monster bestiary, we're also going to see the PS3 HD assets added to this PC version!

And about the JPN version, I wouldn't doubt if XSEED shares their build with Falcom in the future so that the JPN PC version sees the same improvements in the future. It might be a while, but I'm sure it'll happen sometime down the line.