I minored in economics.

我副修经济学。

I minored in English.

我选修了英语。

I minored in French.

我选修了法语。

I minored in literature in addition to art.

我除了辅修艺术以外还辅修文学。

I majored in Economics and minored in Chinese.

我的专业是经济，辅修了汉语。