Change directory to the package you want to proofread. For example,
cd ~/myproject/system-config-printer/
Convert the .po file to a .mo file using msgfmt with -o option:
msgfmt -o system-config-printer.mo ja.po
As a root user, overwrite the existing .mo file in /usr/share/locale/lang/LC_MESSAGES/.
First, back up the existing file:
su -
cp /usr/share/locale/ja/LC_MESSAGES/system-config-printer.mo system-config-printer.mo-backup
Now move the file converted for proofreading.
mv system-config-printer.mo /usr/share/locale/ja/LC_MESSAGES/
Exit root user.
exit
Proofread the package with the translated strings as part of the application:
LANG=ja_JP.UTF-8 system-config-printer