This old article may help:
http://www.archicadwiki.com/TechNotes/Creating%20Special%20Line%20Types?highlight=%28CategoryJapanes...
Note that you cannot 'explode' text in plan in ArchiCAD. So, you'll either have to draw your text with linework, or you can do some dwg tricks, convert in an external program, etc. (You can use the 3D text object and capture the linework from the 3D window, also. But, depending on the font, the letter(s) may have an awfully lot of line segments.) Keep the strokes for the letter(s) very simple.
As Richard said, take a look at the CW, SS, etc line types that are in the base template.
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB