国内大难题怎么说英语

"Domestic grand challenges" is a good way to describe "国内大难题" in English. Some examples of domestic grand challenges might include issues such as poverty, pollution, inequality, and health care. Other possible ways to describe domestic grand challenges in English might include "major issues facing the country," "pressing national problems," or "significant problems facing society within a country." It's important to note that the specific challenges that are considered "grand" will vary depending on the context and the country in question.