Sounds like you were thinking the same thing as me for the most part! Glad you've got some stuff working.

BigTree 5.0 does include localization support but for the admin side (mostly through 1:1 string translation) and not the front-end. Front end localization is planned for the future, though. We've had very limited bandwidth to push (and BigTree 4.3 has been delayed so long now that it's become 5.0) so it definitely won't make the next release but it is something I'd like to see implemented soon!