Disclaimer: I'm completely CLUELESS about digital cameras.
Ok so here's the deal. My father owns a Lumia 920 and we're looking forward to going on vacations and take a bunch of pictures. He's worried that the phone's built-in camera might not be good enough as he is interested in taking pictures from long distances. We were looking in the internetz today and seems that the CANON EOS 1100D + EF-S 18-55 mm IS II (400€) is the best that we can afford with our budget. What do you think?
that won't be great for LONG distances, but is a good starter camera. You can rent lenses, http://www.lensesforhire.co.uk/ to get the length you need. Whether you get this or a similar Nikon get it as soon as you can so that you can practise a lot and get used to the camera and the controls else you'll miss what you want to shoot.
I've spoken to the lenses for hire guys and they are really knowledgable and really friendly.
Both Nikon and Cannon make really good DSLRs and so it really becomes a personal brand preference if you are new to this. Those not new to DSLRs tend to go with the brand that supports their older lenses. Quality of lense is probably more important than body. The 18-55 mm will give you great pictures. I personally prefer (and have) the 18-200 mm. Its a bit heavier but is one of the best "all around" lenses for those desiring close and long shots. On a side note, I use Nikon because I have older Nikon lenses. Also look for manufacturer refurbished DSLRs. These are cheaper than buying new, will have a warranty, and go through a higher quality inspection than new DSLRs coming off the production line.