tr not replacing apostrophe

Question

I want to convert all apostrophes in this file to X:

Bob's book
Bob’s book
Bob′s book  # (Might look the same but actually different)

The first apostrophe is replaced as expected:

$ cat file | tr "'" "X"
BobXs book
Bob’s book
Bob′s book

But the the two other kinds of apostrophe, strange things happen:

$ cat file | tr "’" "X"
Bob's book
BobXXXs book
BobXX�s book

$ cat file | tr "′" "X"
Bob's book
BobXX�s book
BobXXXs book

How to make it work?

Answer 1

tr works in units of bytes, which means it doesn't work properly for multi-byte encodings like UTF-8. The only solutions I know of are to find a version of tr that supports Unicode, or switch to sed or some other tool that can do string replacement.