VSCode diff with textconv applies it only on the old file

Question

I want to avoid displaying comments in translated .po files, when doing a diff in Visual Studio Code. Following Gettext .po files under version control answer, I do:

# global .gitconfig
[diff "po"]
    textconv=msgcat --no-location --no-wrap

and add a .gitattributes file in my repository:

*.po    diff=po

It almost works, but only on the left part of the part (the old file). The modified file keeps showing the comments and does not wrap lines.

How to make it work on both sides? Thank you for your help.