After created collection is displayed information page. First information is: "Collection created! Your new collection is shown below. You can edit additional settings if you'd like." This information isn't displayed as localized even sentences "Collection created!", and "Your new collection is shown below." are translated in the .po file. "You can edit additional settings if you'd like." is absent in the .po file.
(In reply to comment #0) I forgot that another one string isn't displayed translated on this page: "Add to collection". This string is displayed as tooltip for icon next to heart icon. This string isn't in the .po file. In the .po file is "Add to Collection" string.
Looks like we're good here.
Verified FIXED; I now see: "Kolekcja została utworzona! Poniżej znajduje się Twoja nowa kolekcja. Jeśli chcesz, możesz edytować dodatkowe ustawienia."