I haven't found any explanation of abbreviations on that site, but having skimmed some entries I suppose that inf stands for informal.
I guess the first inf belongs to the German term versieben and the second one to the English to make a mess of.
Edit: How inf possibly was created
If you submit entries to that site, you can add some optional (tag-like) information. There are some pre-built tags that can be used but also a blank field for custom-made tags. inf seems to be a custom-made tag. So maybe the explanation of inf as informal is not globally true on that site.
I think that there is little organization which tags are used and how they are formatted because every user can enter new ones as they please.