What exactly is unclear to you? SMAPI is pretty precise here: "only the top level files will be used"
The way translations work is you have 1 folder ("i18n) with the translation files in it. If that folder has subfolders, SMAPI/the game won't load those.
What you need to do:
- open the folders in explorer (or finder if you work on MacOS) and compare their files
- if there are files in the subfolder which aren't in the top folder, you move them to the top folder ("i18n")
- delete the subfolders
-> problem should be solved.