Hello @cngvng,
This area (including the Paracel Islands and Spratly Islands) is a disputed territory, which should be tagged in the language of the country that actually controls the territory; information about territorial disputes is typically noted in administrative relations and tags. Simply renaming elements to quotes like "quần đảo Hoàng Sa" is a destructive behavior, and does not help on labeling features on disputed territories. Therefore, I have restored some of the damaged data because OSM follows the "de facto" principle. If you still have questions, feel free to communicate.