wxGUI: use 'g.gisenv unset=' to unset GRASS variables

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@52648 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/gui_core/preferences.py

@@ -179,7 +179,7 @@ class PreferencesBaseDialog(wx.Dialog):
             if lang:
                 RunCommand('g.gisenv', set = 'LANG=%s' % lang)
             else:
-                RunCommand('g.gisenv', set = 'LANG=')
+                RunCommand('g.gisenv', unset = 'LANG')
             event = wxSettingsChanged()
             wx.PostEvent(self, event)
             self.Close()