Feature Request

Describe your use case and the problem you are facing

As far as I know, wp-cli i18n doesn't provide an equivalent for gettext's msgmerge command. This command is really useful for updating existing po files by merging a pot template created with make-pot. So, for example, if I add a new __ call in my plugin like this:

$newtranslation = __('Translate me please', 'domain');

I can update the messages.pot file with make-pot, but I have to update existing po files with the new translation by hand.

Describe the solution you'd like

To get around this, I've been calling msgmerge directly to update my po files:

find ./languages -name "*.po" | xargs -I % msgmerge -o % % languages/messages.pot

This merges the new translations of messages.pot into all existing po files in the languages directory. It would be great if the i18n command had a similar update-pos or merge-pot command to accomplish the same thing.