I'm at Warwick for IM, it's not as much work as you'd think. 40% of the year is coursework, 60% exams - there are some easy modules, there are some hard modules. Overall, you can do pretty well if you don't slack off - I know a lot of people that didn't do much work apart from their coursework and got firsts, but they're pretty clever. There are a lot of EU students here so you'd fit in. You don't have to know a language for IM, only for IB (International Business) and you can always take one in 2nd year if that's what interests you.
Between warwick and durham, there's not much differences. However, Warwick specialises in business and they're about to open a £30mn business school building. WBS's reputation is on the rise so I'd recommend you come here, but research it more. Both uni's reputations are solid, but I don't think durham is particularly strong in management.