I finally managed to get it working with the Language Switcher plugin. When I write the post I just use special tags to enclose english and romanian sections. It works, it’s just that it looks a bit weird in the visual editor, the tags are seen in the text. Oh well ..
For blogging on the desktop PC, I mapped some of the function keys on my G15 keyboard to the opening and closing tags so I can write posts faster. On the laptop, I guess I have to add some buttons on the visual editor toolbar.