- They’ve become good friends since last year.
- They’ve moved to Japan since last year.
Are the above two sentences acceptable?
Why don’t you give us your choice first, then we’ll correct you if necessary?
sentence 1 is correct.
sentence 2 should be:
They moved to Japan last year/ a year ago.
We use the past simple because the action of moving is complete.
Do you agree?
Both of your sentences are fine. They both focus more on the fact that something has happened and less on when it happened.
Sentence 2 does not mean that they moved to Japan exactly a year ago; it only tells you that they moved to Japan at some (unspecified) point in time between last year and now. Sentence 2 is just fine with the present perfect.