Translation:I came to Japan last month.
This is largely unrelated to the sentence as a whole but I might have just had a brainwave I wanted to share.
If 先 (sen) (せん) is used for previous, and 生 (sei) (せい) for various types of learners or students, then the word for teacher; "sensei" (先生) (せんせい), in a very literal form, would be "previous learner/student" right?
Occasionally the Japanese speaker will choose the other verb than expected. I wouldn't worry about it too much, though. There's a discussion here: https://japanese.stackexchange.com/questions/1669/what-is-the-proper-differentiation-between-来る-and-行く