Assuming you don’t want to block Russian-speaking people, but Russian-origin connections, use a firewall that updates its mapping of IP addresses to country. Pfsense has such a plug-in. You will definitely want to log outbound block or ignore events.
One possible starting point would be to null route their assigned address space. [1] from the firehol repo [2]. This will not block private proxies and VPN's. A determined person could easily get around this. This does not include ipv6. ttyprintk brings up a good point in that one could also look at header fields to check for Russian language attributes.
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[ 3.4 ms ] story [ 20.5 ms ] thread[1] - https://github.com/firehol/blocklist-ipsets/blob/master/ipip...
[2] - https://github.com/firehol/blocklist-ipsets.git
https://isc.sans.edu/diary/rss/28392