Today i found Jan using x-ray, It was clear to me because my first language is Slovak, and they were speaking croatian which is similar, and i saw that he put this :
http://puu.sh/1t6tm
Which is similar to "Zlato Rovno" which roughly translates to Gold Ahead, He then mined some gold, and proceeded to dig a zig-zag into diamond.
I have at this point banned him for 5 days, but he came on with another account and started speaking foreign again, at which point i IpBanned him for 7 days.
Pics:
[spoiler]
(http://i.imgur.com/cDhRf.png)
(http://i.imgur.com/ybOzM.png)
(http://i.imgur.com/jwT0s.png)
[/spoiler]