This is the source. https://www.trustwave.com/en-us/resources/blogs/spiderlabs-b...
And as far as I can tell they just arbitrarily claim that without evidence. The way they say it also makes it sound like a partial list of blocked languages, based on former USSR countries like Syria.
They famously released Syrian data for free, a month or so later added the Syrian language to the ransomware -
https://krebsonsecurity.com/2019/07/is-revil-the-new-gandcra...
Your links supposed anonymous forum post is better evidence, though it's only evidence on the Syria claim is an unlinked announcement and the actions of a group they guess is related.
> When Russian hackers do target victims in Russia, Moscow’s response is swift and harsh. In 2012, eight men were arrested by Russian police after stealing some $4 million from several dozen banks, including some in Russia. According to security blogger Brian Krebs, “Russian police released a video showing one of the suspects loudly weeping in the moments following a morning raid on his home.”
https://carnegieendowment.org/2018/02/02/why-russian-governm...
Apparently the malware kicked in because I didn’t have a chinese keyboard.
After that a chinese friend helped me install the right app and avoid some pitfalls.
[1]: https://twitter.com/MalwareTechBlog/status/14129099009512202...