After starting smuxi and selecting Preferences, produces:

Exception Type:
System.NullReferenceException

Exception Message:
Object reference not set to an instance of an object

Exception StackTrace:
  at Smuxi.Frontend.Gnome.PreferencesDialog._Load () [0x00261] in
/home/abuild/rpmbuild/BUILD/smuxi-1.0/src/Frontend-GNOME/Preferences/PreferencesDialog.cs:346 
  at Smuxi.Frontend.Gnome.PreferencesDialog..ctor (Gtk.Window parent) [0x00a5b]
in
/home/abuild/rpmbuild/BUILD/smuxi-1.0/src/Frontend-GNOME/Preferences/PreferencesDialog.cs:298 
  at Smuxi.Frontend.Gnome.MenuWidget.OnPreferencesActionActivated
(System.Object sender, System.EventArgs e) [0x0001b] in
/home/abuild/rpmbuild/BUILD/smuxi-1.0/src/Frontend-GNOME/Views/MenuWidget.cs:181 

Installing mono-locale-extras seems to solve it.

Bug ID	955084
Summary	smuxi: opening Preferences produces "System.NullReferenceException" - missing mono-locale-extras dep
Classification	openSUSE
Product	openSUSE Tumbleweed
Version	2015*
Hardware	x86-64
OS	Other
Status	NEW
Severity	Normal
Priority	P5 - None
Component	GNOME
Assignee	bnc-team-gnome@forge.provo.novell.com
Reporter	gour@atmarama.net
QA Contact	qa-bugs@suse.de
Found By	---
Blocker	---