XmTextReplaceWcs(3) on Linux
The text d6e467d19ba5, 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 replaces part of a wide character string in a Text widget "XmTextReplaceWcs" "Text functions" "XmTextReplaceWcs"