Actually, the assertion is that it is a language known to God. Markers of
languages known to humans are great for identifying
human languages. Many creatures communicate in non-human languages... do those methods of communication qualify as "languages" to the linguists?
Who died and made linguists the arbiters of what constitutes "language" anyway?
As for identifying counterfeits, look at the fruit. Is the speaker glorifying God in their natural language? Are they pointing others to God and truth, or to themselves, or worse, to false idols?