The Greek that is translated as “has seen and heard” in English is translated in the Catholic Mandarin Chinese Sigao version with an existing traditional Chinese idiom (成语 / chengyu): suǒjiàn suǒwén (所見所聞 / 所见所闻) or “what I saw and heard (lit. “all seen, all heard”).”
Note that the Protestant Union Version also uses it in John 3:32. (Source: Toshikazu S. Foley in Hong Kong Journal of Catholic Studies, 2011, p. 45ff.)