[Qt] Set the layout direction based on user-configured language

For Arabic and Farsi (and Hebrew and others), the Qt layout direction
was wrong.  Layout direction needs to be set to right-to-left for these
languages, resulting in basically a flipped window (which is the
standard for desktop apps using these languages).

This fix makes the Qt app render correctly in these languages.

Special thanks to Akad for calling this to my attention.

gui/qt/__init__.py

@@ -53,7 +53,8 @@
 from PyQt5.QtWidgets import *
 from PyQt5.QtCore import *
 
-from electroncash.i18n import _, set_language
+from electroncash.i18n import _
+from electroncash import i18n
 from electroncash.plugins import run_hook
 from electroncash import WalletStorage
 from electroncash.util import (UserCancelled, PrintError, print_error,
@@ -86,7 +87,7 @@ def __init__(self, config, daemon, plugins):
         super(__class__, self).__init__() # QObject init
         assert __class__.instance is None, "ElectrumGui is a singleton, yet an instance appears to already exist! FIXME!"
         __class__.instance = self
-        set_language(config.get('language'))
+        i18n.set_language(config.get('language'))
 
         self.config = config
         self.daemon = daemon
@@ -264,6 +265,24 @@ def undo_hack():
 
                 callables.append(undo_hack)
 
+        def setup_layout_direction():
+            """Sets the app layout direction depending on language. To be called
+            after self.app is created successfully. Note this *MUST* be called
+            after set_language has been called."""
+            assert i18n.set_language_called > 0
+            lc = i18n.language.info().get('language')
+            lc = '' if not isinstance(lc, str) else lc
+            lc = lc.split('_')[0]
+            layout_direction = Qt.LeftToRight
+            blurb = "left-to-right"
+            if lc in {'ar', 'fa', 'he', 'ps', 'ug', 'ur'}:  # Right-to-left languages
+                layout_direction = Qt.RightToLeft
+                blurb = "right-to-left"
+            self.print_error("Setting layout direction:", blurb)
+            self.app.setLayoutDirection(layout_direction)
+        # callable will be called after self.app is set-up successfully
+        callables.append(setup_layout_direction)
+
         return ret
 
     def _exit_if_required_pyqt_is_missing(self):

lib/i18n.py

@@ -32,6 +32,7 @@
 
 LOCALE_DIR = os.path.join(os.path.dirname(__file__), 'locale')
 language = gettext.translation('electron-cash', LOCALE_DIR, fallback=True)
+set_language_called = 0
 
 def _(x):
     global language
@@ -60,7 +61,7 @@ def npgettext(context: str, singular: str, plural: str, n: int) -> str:
     return message if '\x04' in translated else translated
 
 def set_language(x):
-    global language
+    global language, set_language_called
 
     if not x:
         # User hasn't selected a language so we default to the system language
@@ -70,6 +71,8 @@ def set_language(x):
         # match.
         x = match_language(x) or x
 
+    set_language_called += 1  # Tally the number of times this has been called
+
     if x:
         language = gettext.translation('electron-cash', LOCALE_DIR, fallback=True, languages=[x])
         return x  # indicate to caller what code was actually used, if anything.