As an example, i have a website which uses the same layout, the content is however different. The first site is in danish, the second in english, even if the content was an exact duplicate, in a different language, then it wouldn't matter.

You should however avoid having duplicate content, if its a site in two different languages, then there won't be a problem. But if you have two sites or more, with the same content, well then you just seam to have wasted your domains. Theres no telling which will get hit by the Duplicate Content Penalty, not to mention that it would be pointless to have multiple sites with the same content.

Your best bet is to redirect one site to the other - it's also easier to administrate!

Google says...
Duplicate content generally refers to substantive blocks of content within or across domains that either completely match other content or are appreciably similar. Mostly, this is not deceptive in origin.
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However, in some cases, content is deliberately duplicated across domains in an attempt to manipulate search engine rankings or win more traffic. Deceptive practices like this can result in a poor user experience, when a visitor sees substantially the same content repeated within a set of search results.
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Duplicate content on a site is not grounds for action on that site unless it appears that the intent of the duplicate content is to be deceptive and manipulate search engine results. If your site suffers from duplicate content issues, and you don't follow the advice listed above, we do a good job of choosing a version of the content to show in our search results.

See here: Duplicate content - Webmasters/Site owners Help

I think redirecting one site to the other is the best option. Since the duplicate content is penalized by the search engines, this could lead to a big trouble.

thanks for your reply...

i will redirect one of my site into another.

you are always welcome, dude.

Excellent Stuff here !!!
Thanks for sharing useful information here....

I agree who heartedly with the permanent redirect suggestions. Your ranking of both sites will be lower because the content is duplicated.