Tsao devoted enormous amounts of time and effort to language learning, becoming very proficient in Japanese, English, and Dutch, and somewhat proficient in Spanish, Portuguese, French, German, and Latin. He also became well known for his studies of early Taiwanese history, which were facilitated by his grasp of Dutch documents. Seeking first-hand accounts
投入大量時間和精神苦學語言，曹永和不僅精通日文、英文、荷蘭文，還略通西班牙文、葡萄牙文、法文、德文和拉丁文，而其最為人所熟知的研究，就是透過對古荷蘭文獻檔案的掌握，所從事的台灣早期歷史研究。