我学过3年的日语。翻译成英文

I've learned Japanese for 3 years.

I learned Japanese for 3 years.

I have learned Japanese for three years.

要分情况
1. 你是最进3年学的(到现在为止)(现在完成时)
I have learned Japanese for three years.
2. 你是以前学的(已经结束)(过去完成时)
I had learned Japanese for three years.
呵呵~~
虽然只有一个词 但还是有差别的

I studied three years of Japanese