Greasy Fork is available in English.
When you click on "+ Add to" (for adding a new video to a playlist) YouTube displays the playlists -by default- in a strange order: beginning with the one selected last. This script arranges your playlists alphabetically, making it easier for you to find the one you are looking for.
Si crees que este script incumple las normas de Greasy Fork, puedes denunciarlo para que otros lo borren.