I think what made the change was the Danish series The Killing (originally Forbrydelsen). We love our murder mysteries over here, but The Killing broke the mould. Where a UK show would feature one or more murders in each one hour or two hour programme, the first series of The Killing took a leisurely 20 hours of programming to examine the impact of a single murder. We saw vastly more of how ordinary lives were changed by what had happened. And we also saw in Sarah Lund a police officer main character who frankly made rather a lot of mistakes. Add in the parallel track of political intrigue and the slightly exotic, familiar-yet-not-familiar nature of Denmark and it was a surprise winner.
The success of this programme in the UK made programmers sit up and take notice. And it made audiences - at least in the chattering classes, who perhaps had dipped their toes into foreign language films (who doesn't love Amelie?) - realise that it was worth the investment of concentration. Because, of course, subtitles kill the ability to do other things while you watch. It's difficult to fiddle with Facebook, because as soon as you miss the screen you lose all meaning (unless it's one of those strange sudden bursts of Danish that sound almost entirely like their English equivalent).
So, at the moment, we are getting our doses of foreign (as it were) from the second series of The Killing, avidly watched from Netflix, and the hugely atmospheric French drama The Returned about to reach its climax on Channel 4. What will be next, I wonder?
Image from Wikipedia