Good news! Pre rooted I9100XWLS8 stock ROM is now available. So, you can finally have root on Galaxy S2 4.1.2 XWLS8 firmware that is being rolled out to International Galaxy SII devices. The update I9100XWLS8 for Spain (FOP) is already available for download and can be flashed using Odin. Now you can flash the pre-rooted XWLS8 on Galaxy S2 I9100 device of yours. However, you will have to install busybox separately from the Play Store.
Flash Pre-Rooted I9100XWLS8 & Root Galaxy S2 4.1.2 XWLS8
WARNING: Continue at your own risk. We will not be responsible if your phone falls in shit.
Step 1: Backup your data and important files before continuing.
Step 2: Download the pre-rooted ROM: I9100XWLS8_I9100XXLS8_I9100FOPLS3_root.zip
Step 3: Flash the pre-rooted stock Jelly Bean 4.1.2 on Galaxy S2 using our step by step guide: how to install stock ROM using Odin.
If you do not want to flash the pre-rooted firmware, you can install the stock I9100XWLS8 on your device and wait till the CF-Root for XWLS8 or any other tool becomes available that lets you root your device and install CWM Recovery on SGS2 running Jelly Bean.