Berlin to Interloken

Barb, its actually "Interlaken" which you need to spell right when looking for train schedules. It will take you a whole day to get there from Berlin, so essentially you would have one day there. Thats too short for me. I'd save it for another trip.
You can see the mountains from Interlaken, but you're not actually in them. Most people would likely recommend you not stay in Interlaken itself, but further up the valley in Wengen, Lauterbrunnen or Mürren. But that also adds to your long day of travel.

You don't say when your travel is. You can often get large discounts on rail tickets by buying in advance. Flying from Berlin to Zurich, might be an option but may not save much time, when you consider the logistics of getting to and from the airports, going through security, etc.

When Stan says "a whole day," he means it. Train travel time from Berlin to Lauterbrunnen is 10 hours. And from there to Paris is 6 hours. If you check flight prices from Berlin to Paris at www.skyscanner.com, you'll probably find them an attractive option. Pretty much everyone can use another day in either of those cities.

Looking Up Train Schedules and Routes Online gives you the Deutsche Bahn train schedule link and tips for using it.

Do NOT spend 10 hours getting to Interlaken for only two nights. Not only is Interlaken not where you want to be, but if the weather is not good (and mountain weather is very unpredictable and very changeable), you will have come a long way and spent a lot of money for nothing.

Either allot more time for the mountains and actually stay in them (Lauterbrunnen, Gimmelwald, Mürren, or Wengen), or skip them and put your time and money to something else.

Fly to Zurich from Berlin and then take the train to interlaken.
Buy this plane ticket in advance if you want to get the cheapest fares.
Use Booking.com to search where to stay in Interlaken. That site has hotel reviews from customers.
Review a guide book on sites to see near Interlaken.