Nice project, eagerly waiting to hear it!
About the replaced parts, are the dialogs on the center channel only, and music outside that? In that case, it should be “trivial” to replace the center channel with localized versions!
On a two channel downmix, it is very easy to do just that. However on the 6 channel version, the vocals are one center but the music is heard on all the other channels (including an echo-y delay on the RL RR channels). If I were to just mute all 5 channels and put the correct music in, you’d notice right away when your surround sounds sounds ‘wrong’.
It sounds like trivial issues but I think about sound mixing a lot…
After the lengthy time it has taken to get the 5.1 version ready for release I might just release my 2 channel draft version to you all first, and subsequently release the 5.1 version when it’s ready.