shell interaction (may be added by regedit…)

Good point. You could run a batch script afterwards that set up the registry links.

Or, you could do a normal silent install in English, then copy/unzip a pre-built %AppData%\Notepad++ folder with the language selected for the user

I believe that Notepad++ installer uses NSIS. According to their documentation at https://nsis.sourceforge.io/Which_command_line_parameters_can_be_used_to_configure_installers, the command-line options included /S (silent) and /D (installation folder) – which you found already – and /NCRC, which skips a CRC check during installation.

There are not any other options which I am aware of.

In theory, you could create an issue to request that another option be added to the installer… but given that it’s a pre-built library to create the installer, I don’t know whether the developers could add such an option to the automatic installer. It wouldn’t hurt to ask.

I assume this is for automatic deployment across an organization, otherwise answering the prompts once wouldn’t be worth trying to get around. If that’s the case, then in the mean time, you could do a single manual install on one machine, then zip up the c:\program files\notepad++\ and %AppData%\Notepad++\ folders, and build your own zip (or self-extracting-zip-based exe) that will put your pre-configured Notepad++ in the same location on all the machines you will be deploying to. Maybe not ideal, but it allows full customization (and you could even then decide which extra plugins to automatically include for all your users).