wxPython snap doesn't show text

I have been attempting to use wxPython in a simple snap for a few months now,
and I’ve managed to get a widget appear on screen, but the text is broken,
and running the snap raises multiple errors. I have attached an image of the
messagebox that shows up on screen, clearly broken. My snapcraft.yaml file
is as follows:

name: sqab-tuxbert
version: '0.1'
summary: SQAB - Statistics Quack Asparaguus Bologne
description: |
  Prints a simple message using wxPython.

grade: devel
confinement: devmode

apps:
  sqab-tuxbert:
    command: desktop-launch $SNAP/bin/sqab
    plugs: [desktop, x11, wayland, home, desktop-legacy, opengl]

parts:
  sqab-tuxbert:
    after: [desktop-gtk2]
    source: https://github.com/tuxbert/sqab.git
    plugin: python
    build-packages:
      - libwebkitgtk-dev
      - libwebkitgtk-3.0-dev
      - unity-gtk2-module
      - unity-gtk3-module
      - unity-gtk-module-common
      - unity-gtk-module-autopilot
      - libjpeg-dev
      - libtiff-dev
      - libsdl1.2-dev
      - libgstreamer-plugins-base0.10-dev
      - freeglut3
      - freeglut3-dev
      - xorg-dev
      - libglw1-mesa-dev
      - libglw1-mesa
      - libgtk-3-dev
      - libgtk-3-0
      - libglu1-mesa
      - libgl1-mesa-dev
      - libglib2.0-dev
      - libgtk2.0-dev
      - libnotify-dev
      - libgstreamer1.0-dev
      - libgstreamer-plugins-base1.0-dev
      - gstreamer1.0-plugins-base
      - libcanberra-gtk-dev
      - libcanberra-gtk-module
      - libcanberra-gtk3-0
      - libcanberra-gtk3-dev
      - libwxbase3.0-dev
      - libwxgtk3.0-dev
      - libwxgtk-webview3.0-dev
    stage-packages:
      - libgtk2.0-0
      - libwxbase3.0-0v5
      - libwxgtk3.0-0v5
      - libwxgtk-webview3.0-0v5
    python-packages: [wxpython]

It manages to snap without problems, but upon running, I get a message like
this:

Gtk-Message: Failed to load module "unity-gtk-module"

(sqab:2510): GdkPixbuf-WARNING **: Cannot open pixbuf loader module file
'/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache': No such
file or directory

This likely means that your installation is broken.
Try running the command
  gdk-pixbuf-query-loaders >
/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache
to make things work again for the time being.
Gtk-Message: Failed to load module "canberra-gtk-module"
Gtk-Message: Failed to load module "canberra-gtk-module"

(sqab:2510): Gtk-WARNING **: Could not find the icon
'dialog-information-symbolic-ltr'. The 'hicolor' theme
was not found either, perhaps you need to install it.
You can get a copy from:
    http://icon-theme.freedesktop.org/releases

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed
Gtk-Message: GtkDialog mapped without a transient parent. This is
discouraged.

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): GLib-GObject-CRITICAL **: g_object_unref: assertion
'G_IS_OBJECT (object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): GLib-GObject-CRITICAL **: g_object_unref: assertion
'G_IS_OBJECT (object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): GLib-GObject-CRITICAL **: g_object_unref: assertion
'G_IS_OBJECT (object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): GLib-GObject-CRITICAL **: g_object_unref: assertion
'G_IS_OBJECT (object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): GLib-GObject-CRITICAL **: g_object_unref: assertion
'G_IS_OBJECT (object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): GLib-GObject-CRITICAL **: g_object_unref: assertion
'G_IS_OBJECT (object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): GLib-GObject-CRITICAL **: g_object_unref: assertion
'G_IS_OBJECT (object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): GLib-GObject-CRITICAL **: g_object_unref: assertion
'G_IS_OBJECT (object)' failed

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): Gtk-WARNING **: Error loading theme icon 'image-missing' for
stock: Icon 'image-missing' not present in theme ubuntu-mono-dark

(sqab:2510): GLib-GObject-CRITICAL **: g_object_ref: assertion 'G_IS_OBJECT
(object)' failed

(sqab:2510): GLib-GObject-CRITICAL **: g_object_unref: assertion
'G_IS_OBJECT (object)' failed

···

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