另一门外语用英文怎么说

"Another foreign language" 用英语说为 "another language"，"another" 意为 "另一个"。

这是一个非常简单直接的表达。

例句：

I want to learn another foreign language. (我想学习另一门外语。)
She speaks three languages, including Engpsh and another foreign language. (她会说三种语言，包括英语和另一种外语。)