ui/gtk3: Hide XKB engine but enable it in Plasma Wayland

IBus just cannot defer key events to the secondary input methods
to switch XKB keymaps in Plasma Wayland because IBus has to handle the
compose keys before defer the key events.

Also update the POT file.

BUG=rhbz#2088656

data/dconf/org.freedesktop.ibus.gschema.xml

@@ -223,12 +223,12 @@
     <key name="use-custom-icon" type="b">
       <default>false</default>
       <summary>Use custom icon</summary>
-      <description>Use custom icon name for language panel</description>
+      <description>Use custom icon name for arrow buttons on candidate window</description>
     </key>
     <key name="custom-icon" type="s">
       <default>'Adwaita'</default>
       <summary>Custom icon</summary>
-      <description>Custom icon name for language panel</description>
+      <description>Custom icon name for arrow buttons on candidate window</description>
     </key>
     <key name="use-glyph-from-engine-lang" type="b">
       <default>true</default>