Is is safe to edit language files from wp-content/languages/plugins/woocommerce-ro_RO.mo(.po) ? I'm asking this because I don't want them to be overriden on plugin update. Sorry if dumb question.
This IS safe and this is where custom translation files need to be so that when the main plugin updates itself, your custom translations don't get overwritten.
The previous answer is not correct, simply because the person did not read your folder path correctly. The plugins store their language files (the ones that get overwritten) in this folder
the folder that stores your custom translations, and the one you asked about, is
these do not get touched when a plugin updates itself