留学英语的表达主要涉及“study abroad”这一核心短语。这个短语指的是前往母国以外的国家进行学习，可以是短期或长期的学习经历。例如：“Over the years, hundreds of overseas students have studied at that university.”

当描述朋友留学时，可以使用以下例句：

1. “My friend is planning to study abroad next year.”

2. “She has been accepted into a prestigious university in the United States to pursue her master's degree.”

3. “Studying abroad can be a life-changing experience.”

在写作时，可以根据具体情境选择合适的表达方式，例如描述留学的原因、目的、经历或感受。同时，注意使用准确的词汇和语法结构，以确保表达清晰、准确。

此外，还可以根据具体需求，结合其他相关短语和表达方式，如“overseas student”（留学生）、“exchange student”（交换生）等，使文章更加丰富和具体。例如：“She is an overseas student majoring in computer science.”