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Rylas,
I don't believe it does effect the SEO as long as you are serving up the content properly. I wouldn't do a css attribute of display:none to any of the content you don't want to show. Also write the mobile version for the user not for Google. Make it clean and easy to understand.
*Link for other ways to 'hide' content
http://css-tricks.com/places-its-tempting-to-use-display-none-but-dont/
In the past I have had it all on the same domain using WordPress and WPML. It is a paid plugin but It makes your life as an admin so much easier! The way I would set it up is through **.se/english **(easily accomplished in WPML).
In WPML you can do the translations yourself or submit the articles to a translator through the plugin.