Unicode character:
U+0445 (1093) х CYRILLIC SMALL LETTER HA

If you need some cyrillic characters to reproduce, enter 0445 then hit Alt+C in Microsoft Word, or go to http://translit.cc/ and type some random words, then copy and paste

идеасман хД --> ideasman xD

Thanks, Sebastian! In that particular case I didn't need that character, it was there by mistake. And I spent some time trying to figure out what was wrong. Acually, this problem pops up every now and then because I use something like "1024x2048" in texture's name sometimes. So I decided to report because it could be helpfull for someone.

I couldn't quite redo the problem on Linux/Mac, did not try Windows yet. Is that what you are using?

What I see here is indeed that the image assigned to the plan is not being loaded, but it also does not load in e.g. the image editor. Can you confirm if it is purely a cycles problem or if it also happens in other places in Blender?

Here the image has file path "texture_х.png", but the file in the zip is named "texture_å.png" (a with a circle over it). Using that file works here, and also renaming the file with a cyrillic x in it seems to go ok.

Yes, I'm using Windows. I've encountered this problem on two machines with Win 7 64 bit RUS and Vista 32 bit RUS installed.
Please, take a look at the attached screnshot with the image correctly shown in 3d viewport in texture mode and as solid black in rendered mode.

You're right, it seems to be not only the Cycles problem. I've attached the same scene but with Blender Internal Render setup.
As you can see on the screenshot, the image (wich I've renamed using only a cyrillic letter "Ф" so nobody could get confused ) is loaded properly and is visible in material preview but still rendered black.

This turns out to be a bug in OpenImageIO, fix is being worked on here:
https://github.com/OpenImageIO/oiio/pull/352

This should be fixed now in the latest windows builds, on e.g. builder.blender.org.