I do not manage to import in a library of photo from another library since 10 days

What is the exact error message in the original language? You wrote " either Photo tells that the library to be imported must be cured" . The word "cured" seems to be not the right translation. Could it be, that the message has been "The library needs to be repaired, or updated?

Photos cannot import a library while still running macOS 10.14 Mojave. You need at least macOS 12 Big Sur or later. Is that the system version you are using?

Also, you cannot import from a Photos Library that is syncing with iCloud Photos.

Where are your Photos Libraries stored? Is one of them on an external volume? Then you may want to check, if the external volume is compatible with Photos. Both libraries should be on a volume with the file system format MacOS Extended (Journaled) or APFS, the external volume must not have been used for Time Machine Backups and needs a wired connection - it must not be a NAS: Move your Photos library to save space on your Mac - Apple Support

Is it correct that you are using Mac OS 10.14 Mojave? For that system people often use a 3rd Party software called PowerPhotos to merge Photos Libraries. It's very useful for many things-- I keep it open all the time while I use Photos.

It is good to repair your Library. Waiting 10 days is way too long! Something is wrong. Try starting your computer in Safe Mode to prevent some potentially harmful process from interfering. The method to start in Safe Mode depends on the computer, so see this:

           Start up your Mac in safe mode - Apple Support 

And then see if you can repair the Library.

Let us know if that helps. If not, there are other things to try.

You're welcome. Great that you could solve the problem. 😊