Hi tomasbarao, I did some research but could not find a way to import a .po file to the WordPress Translation Service. I’m afraid the only solution is to copy-paste. Note, though, that some strings were changed and others added in the latest release of the plugin (from a few days ago), so those strings will have to be re-translated (or added).
Thank you again for taking the time to translate the plugin, it is greatly appreciated and I’m sure it will be really useful for all Portuguese users.
Your next steps (if you still want to submit your translation): go to the plugin translation project (https://translate.www.ads-software.com/projects/wp-plugins/improved-save-button) and click on the language you want to translate. Click on “Stable (latest release)” and start submitting the strings (please note that some strings may have changed since the last update, so be careful when copy-pasting from your .po file if it was made before the latest release). The translations would then have to be approved by a PTE (Project Translation Editor) of the language.