When you make a move in po-file or texi-file, the reference follow you automatically in another window.
You are moving in po-file (org-ja.po), and the reference (texi-file, org.texi) in another buffer follows you.
You are moving in texi-file (org.texi), and the reference (org-ja.po) in another buffer follows you.
See assist-po-mode.el