How to say "eloquent" in Japanese

• 口達者くちだっしゃ
  na-adjective, nounCovers 'eloquent' in the sense of a smooth, fast talker. It fits a born talker, fluent and persuasive in conversation, though its 'glib' and 'talkative' senses often give that fluency a glib edge.
  セールスマンは大抵たいてい口達者くちだっしゃだ。↗

  Salesmen are usually fast talkers.
• 宛転えんてん
  taru-adjective, adverb (with と)An uncommon word for speech that is smooth-spoken and sonorous: eloquence as fluent, flowing, pleasant-sounding delivery. For everyday 'eloquent' it is seldom the word you want.
• 口八丁くちはっちょう
  nounChiefly means voluble — a ready, fluent talker who can hold their own in any conversation. For weighty, moving eloquence it is seldom the word you want.
  彼かれは手て八丁はっちょう口八丁くちはっちょうだ。↗

  He is as ready to talk as to work.
• 爽やかさわやかJLPT N2approx.Common
  na-adjectiveA common word best known for 'refreshing, crisp'; of a voice it means clear, of speech fluent. Its link to 'eloquent' is marginal — it suits clear, refreshing speech, not persuasive eloquence.

None of these is a neutral, all-purpose 'eloquent': 口達者 and 口八丁 picture a glib, voluble talker, 宛転 smooth, sonorous speech, and 「爽やか」 clear, refreshing speech, so choose by the shade you mean.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 口達者くちだっしゃeloquent
• 宛転えんてんeloquent
• 口八丁くちはっちょうvoluble
• 爽やかさわやかclear (voice)