The 2L soft drinks are probably available, but I just never buy any of them. Milk, juice and yoghurt come in one liter packages.
As far as soft drinks go bottles like these http://www.premierexports.co.uk/1595-2155-thickbox/diet-coke... are as far as I know standard across all of Europe and they are 2 liters.
* 12 fl oz (355 mL) aluminum can
* 20 fl oz (591 mL) plastic bottle
* 2L plastic bottle
Depending on the brand and store availability I've also seen 12 fl oz glass bottles, 1L bottles, and sometimes smaller sized cans as pretty standard sizes. Other types of drinks (such as energy drinks) can vary in what containers they use.
In general, though, if you're buying soda for a family or for more than one drink/meal, you're going to be buying a 2L bottle (and refer to it as such).