You will find out when you turn up for stage 2 and are given the overview of the scheme and how it runs that many dont get passed stage 1 (application). So no matter what happens be proud that you manged to get to stage 2. You have obviously done something right over the past few years.
Secondly dont worry to much about your english - of course it needs to be at a good standard and as previously stated if you talk as good as you write you should be fine.
Dont feel you are going to get a grilling in the interview the people that do the interviews are very nice indeed and will put you at ease, they are very sincere and look to pass people not to fail them. If you read this forum you should do fine - think of the interview as something to be enjoyed as you have the opportunity to show someone how good you are and the knowledge that you already have - you dont get that opportunity very often!!
Best of luck.
MBA.