Default HTC Mozart language change doubts - pls help

Hi there, I've read tons of information and I'm still confused what to do... Please guys I'm desperate to fix that phone

I've htc mozart 7 in following configuration:
os ver: 7.10.8862.144
fw: 2250.21.51205.707
bootloader: 5.12.2550.5

The only language i can choose now is English (greyed out) which for me is fine but the thing is the phone is gonna be for my mum hence I need to have PL (polish) language in it. I'd like to flash it with stock European rom (I found out i need something with 401 in the rom file name) i guess currently i can not do that as my one is 707 (asia market). So what do I do? I want to permanently change the region for HTC europe (401) so it's not gonna change during connecting to zune or whatever.

Is my way of thinking correct? - To flash different region rom i need to have HSPL -> to do that I have to downgrade the bootloader as current one 5.12 does not allow for using HSLP tool which only supports booloaders from 1.xx -3xx -> to do that the only way to downgrade is GoldCard method. -> for goldcard downgrading i need to have asian rom (707) RUU_Mozart_hTC_Asia_WWE_1.28.707.03_5.52.09.16_22. 33a.50_RELEASE.exe . After all of this and having HSPL, am I free to use an official newest HTC europe update ???? let's say this file: RUU_Mozart_S_HTC_Europe_5.13.401.01_5.71.09.02a_22 .51.50_RELEASE.rar ???

Please if I'm wrong correct me can't wait to have it done ASAP. Thank you!