Well, I managed to take a look at the Russian-language version of DCS A-10C, and unfortunately the JTAC is still in English (as is AWACS, oddly enough).
So, what would have to be done to enable JTAC on the Russian side? It'll have to use the current English voices, unless a Russian community member wants to help out with recorded voices...
The key I have set to the advanced radio options is LCtrl + \, but that may be different on your system.