I have also encountered this bug (also curses, linux, very recent self-compiled game) and did some poking around. It seems the issue here is that the world name prompt, when presented with a character that does something special (in this case, tab) appends that character to the world name in addition to doing whatever it is that character should do. Pressing tab appends a tab character to the world name, then checks whether the world name is valid before trying to finish things and shows you that error message because you're not allowed to put tabs in a world name.

When I rebound world creation to x, it just appended x to the name before asking me whether I was sure.

The function in question is, I believe, worldfactory::show_worldgen_tab_confirm, which I believe calls string_input_popup::query_string to handle input. I cannot truthfully say I understand either function well enough to feel comfortable editing them.

I recompiled the game and can still reproduce the bug.

could you check whether latest changes are pulled? could you specify the commit the build is based on?

Yes, I have of course pulled the latest changes. I'm on commit 8beb2d5 and this is reflected on the title screen.

Also, the bug doesn't happen if the world name is already the maximum possible length.

Yes, I have of course pulled the latest changes. I'm on commit 8beb2d5 and this is reflected on the title screen.

i'm sorry, but the screen is borderless and doesn't seem to contain commit hash

Oh, I didn't mean in the screenshot; the commit hash is obscured by the world creation screen there. Here's a new screenshot.