Here's a comment that I think indicates a basic shibboleth failure:

I have long suspected that the account named "user2501323" is too influenced by the Russian propaganda to be taken seriously, but I don't have any evidence that it is a state actor. Even if it is a Russian Federation resident who is simply too influenced by the Russian state-owned media, I am not sure how we should treat it.

But first, why is this a shibboleth failure? The word "spellings" seems completely out of place here. Even if it's a foreigner living in the US, they would be more likely to know what the word "spell" means (because they would often have to spell words out) -- not less. If the word is back-translated to Russian and then back to English in Google translate, it comes back as "writings". Which points to someone who translated a foreign word for "writing" into English using some automation tools without realizing the significant different between meanings of "write" and "spell" in English. The language in which this was written originally does not have a difference between the sentences "how do you write XYZ" and "how do you spell XYZ".

Of course, this original foreign language could in theory be anything, but given how this account does nothing but advocate for the position taken by the Russian Federation, I think it is a reasonable guess to think that the original language of the comment was Russian.

The 2nd piece of evidence in this comment (and it's not as much a shibboleth as it is a profound misunderstanding of the US system of government) is that he called fmr General Mattis a "fired defence minister". Mattis was a Defense Secretary. There are no "ministers" in the US. In fact, I saw a question either on politics.SE or english.SE about the distinction. This is a marker of someone who is not familiar enough with how the US government positions are commonly described, but who is familiar with how they are described in some parliamentary system (which usually does have "ministers").