Are you trying to convert a pdf file to any other format in Russian language or just want to read the current document in Russian?
What is the original language of the document and Adobe Reader application that you have installed on your computer?
If you are trying the conversion online via web browser- https://cloud.acrobat.com/exportpdf you should see the option during conversion.
You can not do that only with the free version of Adobe Reader. It works with the document cloud subscription (Adobe PDF Pack, Export PDF). Also, if the you have the Russian font installed in your system, otherwise the conversion will automatic pic the native language.
Hope this helps.