Most everyone in Helsinki speaks English - I had no problem communicating with anyone on my trip there last year. There are all kinds of great design shops & museums. I loved going to Marimekko as well as some smaller shops along the Esplanade. Also liked the Kiasma Contemporary Art Museum. I stayed at the Klaus K Hotel and loved that as well (very design oriented).

Design museum is in Korkeavuorenkatu (katu=street): http://www.designmuseum.fi/main.asp?sid=1&sivu=4&kpl=3
And no, you don´t need a translator.

Assume everyone there will have a goo working knowledge of English. Just try to be careful about using idioms which may be specific to your country - those might not be understood.

(It can be tricky if you speak British English and the hearer learned American English - or vice versa.)

nytraveler – you are so right about idioms. I find English speakers (which I am one) just wheel away (I just did it) using idioms, slang and often speak very quickly. It is very much appreciated if you slow down and use simple words. The concepts can be complex, just simplify the wording.

My experience is that the Finns speak very good English, our idioms make us look like gibbering fools