A recent Q concerned the use of "fair enough" at the termination of a conversation/ debate-cum-argument about Brexit, or extending the Empire, or whatever. The OP (What does OP stand for?) advised a Russian colleague, presumably the rest of us, to ask a new Q if we wished to pursue this. What was required, here, was a quote from the literature. Overwhelmed at the prospect of such a search, deployed initiative, a pithy aphorism: "(id est) iustum" giving "well-grounded"; "well-deserved". The OP was, quite naturally, disgruntled; but, failed to respond to the follow-up--how would a Roman have interpreted this; if the Latin is incorrect, why is it?
English and Latin tend to express general evaluations differently. English prefers a substantive; Latin uses an adverb.
That's right! = recte
Good job! = bene
That's true! = vere
If I saw id est iustum in Latin, I would expect the id to connect to a relative clause that would provide further elaboration.
E.g., Id est iustum, quod in lege ponitur. (What is written in the law is just.)