The zip/installer from CELSYS has some double-byte characters in the files names, so they don't extract correctly on non-Japanese systems.
This mainly affects Windows.
Here's some instructions on how to correctly extract from the CSP_100w_app.zip:
[1] Install
Microsoft AppLocale [2] Download the AppLocale patch
[site link] or
[direct link] and copy/overwrite the AppLoc.exe into C:\Windows\AppPatch\
[3] Install
7-Zip (
Note: it has to be the
x86 version otherwise applocale won't function correctly.)
[4] Open AppLocale (should be in your Start Menu).
Click Next.
With 'Launch an application' selected, click Browse.. and find 7zFM.exe (usually in C:\Program Files (x86)\7-Zip).
Click Next.
Language of the application: 日本語 (Japanese - it's usually at the bottom of the menu).
Click Next.
Tick 'Create a shortcut ...'
Click Finish.
[5] Open your Start Menu and you should see a new shortcut in Microsoft AppLocale - 7zFM (7zip File Manager)
Click 7zFM - you now have a Japanese 7-zip capable of reading double-byte characters!
[6] Find your original CSP_100w_app.zip and extract it to a folder.
All the file names are now correct and can be seen by the installer.
You can now run Startup.exe to install CLIP STUDIO PAINT!
Enjoy