I'm trying to create an icon theme for Inkscape inspired by the icons in MS Office so that it looks and feels a bit more native on Windows. But I found that Inkscape doesn't load some custom icons:

document-new.svg

document-open.svg

document-print.svg

document-revert.svg

document-save.svg

and probably others (like save as and revert)

According to the source code those icons have been removed , but I haven't found what icons Inkscape uses for these now. How can I replace those icons?

Thanks and greetings, Robert

Welcome to the forum!

That's about all I can say is welcome.  As far as I understand, the icons Inkscape uses come from different places.  I think in the upcoming version 1.0, there will be some changes with that.  But others will be along shortly, to give you more concrete details.

Inkscape uses gtk icon themes (which follow the freedesktop icon naming specification).

Some icons that are used are not specific to Inkscape (like the ones you mentioned) so they're not shipped alongside the Inkscape icons but are taken from a built-in icon theme. In 0.92.x this is the so-called "hicolor" icon theme. You might be able to overwrite those icons by copying into the folder "icons/hicolor", but I've not verified that.

Thanks for the help so for, I found some solutions for the action icons (save, load, copy, paste, ...). But so far I haven't been able to replace the inscape preferences icon (rightmost icon in the toolbar, a screwdriver and a spanner/wrench. It should be called "preferences-system.svg but I haven't found the correct folder/category for it. (See below).

As for what I found out so far:

The gtk icons that are taken from the gtk theme (under Linux) are not being replaced by icons in /inkscape/share/icons but can be replaced, as mentioned, by icons placed in icons/hicolor/. There the icons need to be placed in the folder with the correct sizes for the purpose (e.g. 48x48) and there in a folder matching the freedesktop categories (e.g. "actions")! That has worked for the action icons but I haven't found the correct folder/category for the preferences icon. The possible ones are "applications" (unlikely) and "categories" (likely). But it doesn't seem to work.

I think this problem could be fixed for 1.0 - and maybe also for the 0.92.x branch, not sure. There was a problem with the load order, maybe that is affecting the issue that you are seeing.

Late to the party but for anyone else who ends up here, I went through that with the Tango/Adwaita themes a while back. Here was the solution (or at least, the start of one.): https://inkscape.org/forums/beyond/custom-save-icon/