To prepare to leave can be translated as "准备出发" in Chinese. The phrase "准备出发" comes from the Chinese words "准备" (zhǔnbèi) which means "to prepare" and "出发" (chūfā) which means "to depart or leave." An example sentence in English would be: "I'm getting ready to leave for my trip." This could be translated into Chinese as: "我正在准备出发去旅行。"
