谐

Left speech radical — the simplified two-stroke side-form of 言, originally a mouth above a horizontal stroke. Indexes 谐 in the speech-and-discourse family with 说 to speak, 话 words, 谈 to chat, 译 to translate. Anchors the meaning: harmony in 谐 is fundamentally agreement reached through talking together.

Right 皆 supplies the sound — jiē shifting to xié via initial alternation in classical readings. Beautifully, 皆 itself means 'all together, in unison,' which gives 谐 a strong semantic bonus: harmonious is what happens when everyone speaks in agreement. Sound and meaning lock together to give 'all-voices-aligned.'