一年一次或两次用英语怎么说

一年一次用英语可以说作 "annual" 或 "once a year"。两次一年用英语可以说作 "biannual" 或 "twice a year"。
"Annual" 来源于拉丁语 "annus"，意思是 "一年"。"Biannual" 来源于拉丁语 "bi" 和 "annus"，意思是 "两年"。
例句：
The company holds an annual meeting to discuss its financial performance. (公司举办一年一次的会议来讨论其财务状况。)
We have a biannual check-up to ensure our health. (我们进行两次一年的健康检查。)