The J-circumflex reference article from the English Wikipedia on 24-Apr-2004
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J-circumflex

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"Ĵ", or "ĵ", is a consonant and letter in the Esperanto alphabet. Since each letter in Esperanto has a consistent sound, this letter is always pronounced the same; its sound is represented by [Z] in SAMPA and [ʒ] in IPA.

See also: Esperanto orthography, Ĉ, Ĝ, Ĥ, Ŝ, Ŭ