Those “already translated” strings is made by myself cause I was trying to figure it out how to make poedit look like in the guide you described, but I think my poedit version is different from yours. Maybe ubuntu’s default repository is outdated.
For those who are using 1.5.4 version of poedit or can’t find the “Create New Translation” button, here’s my tips:
Click File->New catalog from POT file…->navigate to the pot files inside every folder and select it->edit the “Project name and version” and “Language”(otherwise poedit don’t allow you translate except English lol)->save it as a po file->enjoy your translation!
Although I’ve solved it by myself, thank you lah7 anyway!