Need Help with XPERIA ARC S

[BelleXDesigns]

Hi Guys
I need your help
I have Xperia Arc S lt18i with MIUI v4 official and I want to update it to v5
I have download the official rom from here (180MB)
http://miuiandroid.com/community/threads/3-7-26.21489/
And I tried to flash but I got error and installation aborted
So do I need to download the lang pack (124MB) and add it to the rom???
or download it and add the rom the lang pack??
Please help
And Thanks​