Laudator Temporis Acti

K.J. Dover, in his paper on "Language and Character in Aristophanes," in Greek and the Greeks. Collected Papers, Volume I: Language, Poetry, Drama (Oxford: Basil Blackwell, 1988), pp. 236-248, cites passages from the Athenian playwright where the language is especially appropriate or fitting for the character who utters it. Some of the examples involve dialect or bad Greek spoken by foreigners, and others suit the age or social standing of the speakers in one way or another. Dover doesn't cite the scholia to Aristophanes, but some of them mention the same phenomenon (tr. W.G. Rutherford):

• On Acharnians 211: The poet is quite consistent and altogether perfect in the way in which he reproduces the temper and the style of conversation of old men -- their temper in their irritability, and their style of conversation in the reminiscences of their past life. To us Nestor seems to talk in much the same way.
  
• On Ecclesiazusae 999 (ma ten Aphroditen = by Aphrodite): Being a courtesan, the hag uses this oath.
  
• On Clouds 236 (he phrontis helkei = the thought draws): Strepsiades ought to have said 'the soil draws,' but being a clodhopper he does not take in what is meant, and turns the expression upside down, so making the meaning unintelligible.
  
• On Clouds 257: Strepsiades is a boor and puts Athamas for Phrixus. It was not Athamas but Phrixus who was killed. As a boor Strepsiades might be expected not to know the legends, and he puts the one for the other.
  
• On Clouds 639: Strepsiades answers like a farmer. He takes the question to be of farm weights and measures.
  
• On Clouds 1206: Like the rustic that he is, Strepsiades makes a mistake in the vocative (of his own name).
  
• On Frogs 950: Euripides is also attacked in comedy for assigning quite unsuitable words to his various characters without making any distinction between them.
  
• On Thesmophoriazusae 1083 (lalis = you say): Spelt without the epsilon. The Scythian speaks Greek as a foreigner.
  

These comments in the scholia to Aristophanes are all the more interesting in the light of Plutarch's criticism of Aristophanes for failing to make distinctions of this sort (Comparison of Aristophanes and Menander 853d, tr. H.N. Fowler):

Moreover, in his diction there are tragic, comic, pompous, and prosaic elements, obscurity, vagueness, dignity, and elevation, loquacity and sickening nonsense. And with all these differences and dissimilarities his use of words does not give to each kind its fitting and appropriate use; I mean, to a king his dignity, to an orator his eloquence, to a woman her artlessness, to an ordinary man his prosaic speech, to a market-lounger his vulgarity; but he assigns to his characters as if by lot such words as happen to turn up, and you could not tell whether the speaker is son or father, a rustic or a god, or an old woman or a hero.