The following command has been run to remove strings not present in
gspell:

$ for i in *.po; do msgattrib --output-file=$i --no-obsolete $i; done

The following command has been run to remove fuzzy strings:

$ for i in *.po; do msgattrib --no-fuzzy -o $i $i; done

Then, PO_DEPENDS_ON_POT has been temporarily set to 'yes' in Makevars,
to update the *.po files.

$ cd po/
$ rm gspell.pot
$ make gspell.pot
$ make

Only the translations almost fully translated are kept. This was done
with the following bash script:

for po in *.po
do
        output=`msgfmt --statistics $po 2>&1 | grep "30 translated messages"`
        if [ -z "$output" ]
        then
                git rm $po
        fi
done