OK, I removed all the comments in the messages.json files and that pass.

F.

Here is the link
https://sourceforge.net/projects/skimtheclipboard/files/

Thanks

F.

my extension package is named skimtheclipboard0.0.1.nex
The manifest file has a default locale
"default_locale": "en",
and my _locales directory contains three subdirectories: en, fr, de. Each contains a messages.json file, stored as utf8, and that seems to load properly when I change the language in the browser.
I received "Package name is marked for translation, but there are no valid message files." when I want to upload the nex file in the upload page: https://addons.opera.com/developer/upload/

What am'I missing ?
Thanks for any help !
F.