The software for my Russian Internet connection was coming up all ??????. I only got it to work because the word "PIN" was in European characters so I knew when to type in my number.
The most obvious solution was to install Cyrillic fonts, but I had already done that long ago in the regional/language settings.
The ?????? came up when browsing, or when I'd installed certain software.
I finally found quite a simple solution at the website maintained by the Slavic Languages department at GWU. All you have to do is choose "Russian" as the default for non-unicode languages. I had always avoided doing that because I thought it would mess up the English. Well, it might mess up Spanish or French, but English and Russian are both working like a charm at this point.
I just have to praise their website a little. They put up screenshots showing the exact problem and then describe the exact step-by-step solution. Way to go!