Word or phrase meaning 'Misinterpretation of tone due to language or cultural barrier'

One general-purpose expression comes to mind: 'faux pas'. Or its English-language equivaltent, 'false step'.

A quote from Stevenson's "Virginibus Puerisque":

An orator makes a false step; he employs some trivial, some absurd, some vulgar phrase; in the turn of a sentence he insults, by a side wind, those whom he is labouring to charm; in speaking to one sentiment he unconsciously ruffles another in parenthesis; and you are not surprised, for you know his task to be delicate and filled with perils.

Digging a bit from the 'faux pas' page at Wikipedia, I found the expression "cross-cultural blunder". That may fit the purpose. Or, per Adam Brown's suggestion in a comment below, 'cultural faux pas'.

Perhaps we could call this a failure to adopt an appropriate register.

Your writer might use a register that they believe to be learned or authoritative, but which reads to some as condescending. Register can be very difficult to get right when participating in social media, as expectations vary from site to site. In many cases - I'm thinking in particular of Facebook or OKCupid - a level of ironic detachment and insouciance is essential, or else the writer might read as naive or over-earnest.