I already have following

[attr]POFILE merge=merge-po-files

locale/*.po POFILE

in the .gitattributes and I'd like to get merging of branches to work correctly when the same localization file (e.g. locale/en.po) has been modified in paraller branches. I'm currently using following merge driver:

#!/bin/bash
# git merge driver for .PO files (gettext localizations)
# Install:
# git config merge.merge-po-files.driver "./bin/merge-po-files %A %O %B"

LOCAL="${1}._LOCAL_"
BASE="${2}._BASE_"
REMOTE="${3}._REMOTE_"

# rename to bit more meaningful filenames to get better conflict results
cp "${1}" "$LOCAL"
cp "${2}" "$BASE"
cp "${3}" "$REMOTE"

# merge files and overwrite local file with the result
msgcat "$LOCAL" "$BASE" "$REMOTE" -o "${1}" || exit 1

# cleanup
rm -f "$LOCAL" "$BASE" "$REMOTE"

# check if merge has conflicts
fgrep -q '#-#-#-#-#' "${1}" && exit 1

# if we get here, merge is successful
exit 0

However, the msgcat is too dumb and this is not a true three way merge. For example, if I have

1. BASE version

   msgid "foo"
   msgstr "foo"
   

2. LOCAL version

   msgid "foo"
   msgstr "bar"
   

3. REMOTE version

   msgid "foo"
   msgstr "foo"
   

I'll end up with a conflict. However, a true three way merge driver would output correct merge:

msgid "foo"
msgstr "bar"

Note that I cannot simply add --use-first to msgcat because the REMOTE could contain the updated translation. In addition, if BASE, LOCAL and REMOTE are all unique, I still want a conflict, because that would really be a conflict.

What do I need to change to make this work? Bonus points for less insane conflict marker than '#-#-#-#-#', if possible.