Blogging in different languages

Hello guys. I've been thinking about setting up a blog about some niche subject -- in different languages.
Now should I use different domains for each language, or should I put them all under the same domain just by changing the subdomain?

If I do decide to use different domains, can adsense somehow smell that the content is not original (even if the languages are different)? If so, should I use different themes and structure to avoid this?

@VallacePolo

You should use the correct href lang attributes and there not will be any issues.
The best way is use single domain + languages in subdirectories,
because all link juice will be more effective than on multiple domains.

Cheers, Greg.

Ok, thank you for your input. I guess I'll have to look more into href lang attributes.

Better go for a single domain as said. But spinning/translating the same content and using it over subdirectories isn't a good idea.