If I create a text cell and type some greek text, most of the symbols are italics as if the cell had an Input style. It doesn't happen with latin characters. I recollect that it is impossible to fix it, but I can't find the source where I read it.
Perhaps someone knows a workaround ? The following screenshot is from Mathematica 8/Linux.
EDIT1: I just noticed that writing capital greek letters works fine (the letters are normal, not italics). The following screenshot is from Mathematica 9.0.1/OSX Mavericks.
Does that piece of information ring any bells to anyone on what might be the underlying problem ?
EDIT2: I also found this link describing a workaround by using custom modified unicode mapping files. I can't check it right now as I'm not near my Linux installation.
EDIT3: I did try it though in Mathematica 9.0.1/OSX (although the article talks about Mathematica 7&8/Linux), and it works great! Here is the relevant screenshot:
EDIT4: As pointed out by @ybeltukov in comments, the workaround is to set the third column of
UnicodeFontMapping.tr to 0 (zero) for Greek letters so that the default font is picked for them.
EDIT5: This workaround doesn't anymore apply to Mathematica 10. I cannot find the
UnicodeFontMapping.tr file. There's another effective workaround though, described here in Alexey's answer.