Package icu4c provides libicule.so.

http://slackware.uk/absolute/absolute-c … CKAGES.TXT reads
PACKAGE NAME:  icu4c-56.1-i586-2.txz
PACKAGE LOCATION:  ./absolute/l
PACKAGE SIZE (compressed):  8015 K
PACKAGE SIZE (uncompressed):  34050 K
PACKAGE REQUIRED: 
PACKAGE CONFLICTS: 
PACKAGE SUGGESTS: 
PACKAGE DESCRIPTION:
icu4c: icu4c (International Components for Unicode)
icu4c:
icu4c: The International Components for Unicode (ICU) libraries provide
icu4c: robust and full-featured Unicode services on a wide variety of
icu4c: platforms.
icu4c:
icu4c: Homepage: http://www.icu-project.org/

ls /var/log/packages/ | grep icu4c
icu4c-56.1-i586-2

Roxterm package version from slackbuilds.org is out of date (version 2.9.7) so probably it requires icu4c-51
you need to build roxterm with the source package from https://sourceforge.net/projects/roxterm/ (latest version 3.3.2)
assumed that this version requires icu4c-56 which is installed on Absolute 14.2

on xterm
keyboard key combination Ctrl+Shift+c = copy
keyboard key combination Shift+Insert = paste

I went for mate-terminal and compiled the mate-desktop system from source.

I used this chain:

matedesktop
libmatemixer
libmateweather
matemenus
matepanel
matenetbook
matemedia
marco
libmatekbd
matesensorsapplet
matesettingsdaemon
caja
cajaextensions
engrampa
eom
mateutils
pluma
mateterminal

matedesktop:
url1: http://pub.mate-desktop.org/releases/1. … 9.2.tar.xz
url2: http://pub.mate-desktop.org/releases/?C=M;O=D
libmatemixer:
url1: http://pub.mate-desktop.org/releases/1. … 9.0.tar.xz
url2: http://pub.mate-desktop.org/releases/
libmateweather:
url1: http://pub.mate-desktop.org/releases/1. … 8.2.tar.xz
url2: http://pub.mate-desktop.org/releases/?C=M;O=D
matemenus:
url1: http://pub.mate-desktop.org/releases/1. … 8.1.tar.xz
url2: http://pub.mate-desktop.org/releases/1.18/?C=M;O=D
matepanel:
url1: http://pub.mate-desktop.org/releases/1. … 8.7.tar.xz
url2: http://pub.mate-desktop.org/releases/
matenetbook:
url1: http://pub.mate-desktop.org/releases/1. … 8.2.tar.xz
url2: http://pub.mate-desktop.org/releases/1.7/
matemedia:
url1: http://pub.mate-desktop.org/releases/1. … 8.2.tar.xz
url2: http://pub.mate-desktop.org/releases/
marco:
url1: http://pub.mate-desktop.org/releases/1. … 9.2.tar.xz
url2: http://pub.mate-desktop.org/releases/?C=M&O=D
libmatekbd:
url1: http://pub.mate-desktop.org/releases/1. … 9.1.tar.xz
url2: http://pub.mate-desktop.org/releases/?C=M&O=D
matesensorsapplet:
url1: http://pub.mate-desktop.org/releases/1. … 9.1.tar.xz
url2: http://pub.mate-desktop.org/releases/1.7/
matesettingsdaemon:
url1: http://pub.mate-desktop.org/releases/1. … 9.1.tar.xz
url2: http://pub.mate-desktop.org/releases/1.8/
caja:
url1: http://pub.mate-desktop.org/releases/1. … 9.3.tar.xz
url2: http://pub.mate-desktop.org/releases/1.18/
cajaextensions:
url1: http://pub.mate-desktop.org/releases/1. … 8.2.tar.xz
url2: http://pub.mate-desktop.org/releases/1.7/
engrampa:
url1: http://pub.mate-desktop.org/releases/1. … 9.2.tar.xz
url2: http://pub.mate-desktop.org/releases/?C=M&O=D
eom:
url1: http://pub.mate-desktop.org/releases/1. … 8.3.tar.xz
url2: http://pub.mate-desktop.org/releases/1.7/
mateutils:
url1: http://pub.mate-desktop.org/releases/1. … 9.1.tar.xz
url2: http://pub.mate-desktop.org/releases/1.10/?C=M;O=D
pluma:
url1: http://pub.mate-desktop.org/releases/1. … 9.3.tar.xz
url2: http://pub.mate-desktop.org/releases/?C=M&O=D
mateterminal:
url1: http://pub.mate-desktop.org/releases/1. … 9.1.tar.xz
url2: http://pub.mate-desktop.org/releases/1.8/

You can probably script-create slackware packages for these. I was too lazy
and just mass-compiled them using a set of ruby scripts.

Thankfully absolute linux comes with very recent gtk/glib so I did not really
have to fiddle with that at all. On default slackware, I'd first have to compile
gtk glib pango atk cairo etc...