The Liar Paradox. “Truth” for English sentences is not definable in English.
Proof. Suppose it is. Then so is its complement “False”.
Let s be the sentence “This sentence is false” .
Since the phrase “This sentence” refers to s, we have
s iff “This sentence is false” iff “s is false” iff not s.
Since the sentence is a contradiction, it is false. So I don’t see any problem, it’s true that the sentence is false, and therefore Truth is not definable in English sentences. At least if you agree False is opposite to Truth in English.