Twitter Inc.’s controversial China chief has departed after only eight months, the latest executive to leave amid a global reorganization. A stream of executives has left the company since it announced layoffs in October amid continued losses. Profitability has long been a challenge for the popular social network and its revenue growth has slowed. In a series of tweets on Dec. 31, Twitter’s Managing Director for China, Kathy Chen, announced her departure but said Twitter would keep open its Hong Kong office. “Now that Twitter’s APAC [Asia Pacific] team is working directly with Chinese advertisers, this is the right time for me to leave the company,” Ms. Chen wrote in a tweet.