“当法官”常见的英文表达是 “serve as a judge” 或 “act as a judge”。
“serve as a judge” 强调以法官的身份履行职责、承担相关义务，侧重于正式、长期地担任这一角色。例如：He has served as a judge in the local court for over a decade.（他在当地法院担任法官已有十多年了。 ）
“act as a judge” 更侧重于临时、在特定情境下承担法官的职责或发挥类似法官的作用。例如：During the mock trial, she acted as a judge and made fair rulings.（在模拟审判中，她担任法官并做出了公正的裁决。 ）