I am in the experimental stage right now, after updating from a very old version.
Having quite a bit of experience with language packs, I'm surprised to see that editing messages.po does not impact all templates alike, if at all.
In this case, I edited locales > es-Es > LC_MESSAGES > messages.po (with poedit 1.8.9), which, first of all, did not get rid of the unnecessary "el" plus lacking space before the pub date in the Ark skin, but also keeps adding "posted on" (without translation - in spite of being translated in messages.po) in the Bootstrap_blog skin, as the attached image shows. Top: Ark skin, bottom Bootstrap_blog skin.
Is there something else that rules templates, language packs, translations and/or widgets (small print)?
Thank you!