It describes the process https://translations.atlassian.com/dashboard/download?lang=ru_RU, but I could not find in the Manage add-ons to add a new plug-in with the Russian language. There is no Browse button, so I can download it.
When I try to download the plug-in according to the instructions https://confluence.atlassian.com/display/DOC/Installing+a+Language+Pack, I get the error:
Are you using Atlassian OnDemand/Cloud?
If so, unfortunately, there's no way to change the language to Russian.
Here's Atlassian Documentation on Language Support for OnDemand:
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