Mozo doesn't launch - unknown locale: en_IL

When trying to launch mozo from a terminal window, I get the following:

~$ mozo
Traceback (most recent call last):
  File "/usr/bin/mozo", line 36, in <module>
    main()
  File "/usr/bin/mozo", line 32, in main
    app = MainWindow(datadir, version, sys.argv)
  File "/usr/lib/python2.7/dist-packages/Mozo/MainWindow.py", line 56, in __init__
    self.editor = MenuEditor()
  File "/usr/lib/python2.7/dist-packages/Mozo/MenuEditor.py", line 37, in __init__
    self.locale = locale.getdefaultlocale()[0]
  File "/usr/lib/python2.7/locale.py", line 545, in getdefaultlocale
    return _parse_localename(localename)
  File "/usr/lib/python2.7/locale.py", line 477, in _parse_localename
    raise ValueError, 'unknown locale: %s' % localename
ValueError: unknown locale: en_IL

I've not changed the locale, so it should be whatever was assigned when Ubuntu Mate 18.04 got installed. I've had the same problem in Ubuntu Mate 17.10 and 17.04.

~$ locale
LANG=en_IL
LANGUAGE=en_US
LC_CTYPE="en_IL"
LC_NUMERIC="en_IL"
LC_TIME="en_IL"
LC_COLLATE="en_IL"
LC_MONETARY="en_IL"
LC_MESSAGES="en_IL"
LC_PAPER="en_IL"
LC_NAME="en_IL"
LC_ADDRESS="en_IL"
LC_TELEPHONE="en_IL"
LC_MEASUREMENT="en_IL"
LC_IDENTIFICATION="en_IL"
LC_ALL=

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: mozo 1.20.0-1
ProcVersionSignature: Ubuntu 4.15.0-22.24-generic 4.15.17
Uname: Linux 4.15.0-22-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.1
Architecture: amd64
CurrentDesktop: MATE
Date: Tue Jun 5 00:57:29 2018
InstallationDate: Installed on 2018-04-28 (37 days ago)
InstallationMedia: Ubuntu-MATE 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
PackageArchitecture: all
SourcePackage: mozo
UpgradeStatus: No upgrade log present (probably fresh install)