Install languages

I deleted languages via ftp, but now i want instal it via the back office.

The computer say that cannot instal in the database.

What i do wrong?

When you delete via FTP the files in the lang folder, all you are doing is removing the compiled language files. It does not actually remove the language. Thus they are still installed which is the reason you can't install them again.

All you need to do to get the files back you deleted with FTP is to recompile the languages.