Is to be able to describe something to be able to judge that it's true or not?
Of course, we can say "according to some legend, book, etc, unicorns have four legs", and it's true, but what if I start with "according to reality"?
Let's say, for the sake of argument, that human brains and human minds are objectively real. Then we could say that some concept of "unicorn" objectively exists as information represented in the connections between neurons of the physical brains of most humans (excluding of course those humans who have never being exposed to the concept). Then, it is objectively true according to reality that most human brains would logically conclude that the statement "unicorns have four legs" is consistent with the concept of "unicorn" they had previously learned. This is grounded in the information processing capabilities of biological human brains, which we already conceded are real. We can empirically verify this by testing it with many humans (ask each person on the planet for a definition of "unicorn" and then ask them whether a unicorn has four legs, and record the responses). We can also extend this to artificial systems, such as Large Language Models like ChatGPT, that also have the capacity to represent concepts and then perform logical inferences over them. Again, all this is objectively grounded in real physical systems (brains, computers, etc.) that are capable of representing and storing concepts and reasoning over them.
In other words, I'm suggesting that your question "is it true that unicorns have four legs according to reality?" should be rephrased as "Is it objectively true that if a human brain or a computer with similar reasoning capabilities learns the concept of 'unicorn', it would conclude that the statement 'unicorns have four legs' is logically entailed by the definition of the concept?", the answer to which would be "in most cases, yes, with the exception of information processing systems (brains, computers, etc.) with their cognitive faculties impaired in a way that would prevent them from performing a valid logical inference".