Hi Kolos403, i too have this exact issue, i came across this issue on the 11th of september the same day pioneer released their last firmware update for our unit. i've spoken to Pioneer and Northolt Audio Repairs in middlesex in the UK and neither have been any use to me whatsoever, when i spoke to the engineers at both Pioneer and Northolt i was told i'd have to send my unit in for repair to have the issue resolved at MY OWN EXPENSE! fooking ridiculous!
i can't believe they haven't released a fix this yet, i've emailed naviextras, processed two support tickets and i haven't got much more than, "Your support is being dealt with, please be patient during this time" and i created the support ticket on the 18th. Your the first person i've come across with the same issue, have you found a fix for this yourself or are you still on the hunt for a solution?
I've gone to some extent to try and get the voices and the english language file back, data recovery software, trawling the internet for many many hours trying to find these files are next to impossible, i think the only option is to find someone who has our unit that hasn't used naviextras toolbox yet to send us the files we require from their flash drive, i think thats going to be our only hope.......
Will keep you updated on any developments.