Hi Nils,
If you aren't producing translated content, but are just going to put some posts out in English, I do not believe you will see a problem. You could consider putting the English content into a subfolder like /en/ and including a header such as http-equiv="Content-Language" content="en"> in the head. You could also target that subfolder to an English speaking country in Webmaster Tools, but you can't pick more than one country, so that doesn't seem the right option here (i.e. you'd have to choose the UK, US, or another place, and if you're trying to get visitors from all over the world, that could hinder your rankings in all locations bar the country you choose).
If your entire website is geo-targeted to Sweden, either by a .se domain name or geo-targeting in WMT already, you might have a harder time ranking in foreign countries as Google has been told that the entirety of the site is for the Swedish market. However, on a generic TLD like .com, you should be able to pick up a good amount of search traffic from other markets with English content.