XmTextGetSubstringWcs(3) on Linux
The text 03846c9487e5, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A Text function that retrieves a portion of a wide character internal text buffer "XmTextGetSubstringWcs" "Text functions" "XmTextGetSubstringWcs"