Well if you're applying for two languages you'll have two interviews for each. I applied for French sole though so I had two French interviews.
You'll most likely get a poem/text to read in the language and you'll have 15 or so minutes to analyse it - they give you dictionary (at least at Trinity they do)
The questions asked aren't too wacky, but they do make you think and look closely at language/structure of the text.
They'll probably ask you about literature that you've read in the language (be sure to mention anything you've read in your free time - they want to see passion for literature) Make sure you've really thought about anything you've put down though because they will ask about theme/genre/context/characters - anything really.
The amount of actual French you speak varies I think - I only spoke for about 5 minutes and it was just about my time in France.
My second interview was entirely in English but was a grilling about an extract from some philosophy essay - They seem to love linking everything to literature because I was asked if any book I had read would be relevant to the extract (this caught out some people who hadn't studied much literature in any language).
So overall the message seems to be - show passion for literature in particular but also demonstrate the ability to analyse anything they see fit to bring up, be it stuff about culture or even the nature of language itself. Competence in the language is important (You'll have grammar tests) but you certainly don't have to be fluent.
Hoped that helped a bit, beyond this the actual questions they ask get quite specific to the candidate and so might seem really hard for someone else, but okay for the actual candidate. E.g. I know someone who got asked in French about cello music - but he'd sent in an essay about cellists so I suppose he could handle it