While in London this weekend I heard many different languages being spoken, including different varieties of English, French, German, Spanish, Portuguese, Japanese, Mandarin and Cantonese. Those were just the ones I recognised. I spoke mainly English while I was there, plus some Mandarin and a little Japanese and Portuguese. The next time I’m there I might take my digital recorder to record some of the polyglot babble.
In Bangor you can find speakers of quite a variety of languages, but the linguistic diversity of London and other big cities is much higher, so whatever language you want to practise, you can probably find people to speak with.
There’s a video of part of the Sing for Water concert I took part in here