The Corcyraeans, their city isolated in a war with Corinth, have sent emissaries to Athens to ask for an alliance. Because the Corcyraeans have traditionally been isolationist, their mission is in some embarrassment as they seek help, for they cannot show that they are owed this help. The Corcyraean envoy faces this difficulty forthrightly, as he addresses the Athenians.
‘Δίκαιον, ὦ Ἀθηναῖοι, τοὺς μήτε εὐεργεσίας μεγάλης μήτε ξυμμαχίας προυφειλομένης ἥκοντας παρὰ τοὺς πέλας ἐπικουρίας, ὥσπερ καὶ ἡμεῖς νῦν, δεησομένους ἀναδιδάξαι πρῶτον, μάλιστα μὲν ὡς καὶ ξύμφορα δέονται, εἰ δὲ μή, ὅτι γε οὐκ ἐπιζήμια, ἔπειτα δὲ ὡς καὶ τὴν χάριν βέβαιον ἕξουσιν: εἰ δὲ τούτων μηδὲν σαφὲς καταστήσουσι, μὴ ὀργίζεσθαι ἢν ἀτυχῶσιν.
Proposed translation: It is proper, men of Athens, that those coming to seek help, who cannot prove that they are owed the help by their past deeds or by an alliance treaty, should show first, how what they ask for promises a happy outcome, or at least will not be hurtful; and next, that they will have constant gratitude. If they cannot demonstrate these things, then they should not be angry if their request fails.
Commentary on the parts I had trouble with:
Δίκαιον: “[It is] just/proper”. This is an adjective with the verb to-be implied. In this sentence, it will have an infinitive complement.
τοὺς . . . ἥκοντας: "the ones coming. This denotes the speaker and his fellow emissaries. They are coming to ask Athens for help in a war.
μήτε εὐεργεσίας μεγάλης μήτε ξυμμαχίας προυφειλομένης: Genitive absolute [?], meaning “neither by [earlier] great deeds nor by an actual alliance justified [in their request for an alliance].”
παρὰ τοὺς πέλας: “before neighbors”, i.e. before the Athenians, who are the audience for this oration. Literally, “before the ones-nearby” ??
ὥσπερ καὶ ἡμεῖς νῦν: “just as we [are] now” [in seeking the aid of Athens]
δεησομένους: participle, accusative plural subject of infinitive ἀναδιδάξαι, agrees with τοὺς . . . ἥκοντας, “asking”.
ἀναδιδάξαι πρῶτον: “to show first”
μάλιστα: I left this untranslated, maybe “as well as possible”???
μὲν ὡς καὶ ξύμφορα δέονται: [???] “that they ask for something-expedient, or something-promising-a-favorable-outcome.” I cannot properly explain the grammar of this clause.