Simple commad to search for i18n properties in several folders and move them to a new one
go get github.com/benaich/i18n-migrate
i18n_migrate src dst key.txt
# src/messages_en.properties
feeling.happiness=happiness
feeling.pain=pain
feeling.fear=fear
# src/messages_fr.properties
feeling.happiness=bonheur
feeling.pain=chagrin
feeling.fear=peur
# keys.properties
feeling.fear
i18n_migrate src dst keys.properties
# dst/messages_en.properties
feeling.fear=fear
# dst/messages_fr.properties
feeling.fear=peur