Default P710 Contacts not correctly displaying (Chinese)

I wanted to import my old contacts from my German Sony Ericsson Xperia Arc. I was using a custom rom on the previous phone which supported traditional Chinese (Taiwan).

Now I have a lot of contacts with Chinese characters but when I import them from the internal storage into the address book (contacts) they are just displayed as ???.
Any possibilities to change that? That is most important for me!

I would like to use my Firmware and not update towards to an Asian firmware.
But how can i reset and flash back to StockRom? Not possible, once I start LGMobile Support Tool, it says I have the newest firmware and no possibility to flash back to StockRom.
Phone: LG Optimus L7 II (P710)
Andoird: 4.1.2
ROM: SlimSystem V2.3 JORDAN (Optima Team)
Kernel: 3.4.0
Software Version: P71010j-EU-XX