kivy: locale: set default language based to OS lang

On Android, the default language is now set to the language of the OS,
instead of English.

related https://github.com/spesmilo/electrum/issues/4618
related https://github.com/spesmilo/electrum/issues/7494

electrum/gui/kivy/main_window.py

@@ -28,6 +28,7 @@ from electrum.bitcoin import COIN
 
 from electrum.gui import messages
 from .i18n import _
+from .util import get_default_language
 from . import KIVY_GUI_PATH
 
 from kivy.app import App
@@ -402,7 +403,7 @@ class ElectrumWindow(App, Logger):
         Logger.__init__(self)
 
         self.electrum_config = config = kwargs.get('config', None)  # type: SimpleConfig
-        self.language = config.get('language', 'en')
+        self.language = config.get('language', get_default_language())
         self.network = network = kwargs.get('network', None)  # type: Network
         if self.network:
             self.num_blocks = self.network.get_local_height()

electrum/gui/kivy/util.py

@@ -1,4 +1,4 @@
-from kivy.utils import get_color_from_hex
+from kivy.utils import get_color_from_hex, platform
 
 
 def address_colors(wallet, addr):
@@ -21,3 +21,12 @@ def address_colors(wallet, addr):
     elif wallet.is_billing_address(addr):
         colors = BLUE
     return (get_color_from_hex(color) for color in colors)
+
+
+def get_default_language() -> str:
+    if platform != 'android':
+        return 'en_UK'
+    from jnius import autoclass
+    Locale = autoclass("java.util.Locale")
+    lang = str(Locale.getDefault().toString())
+    return lang if lang else 'en_UK'