kivy: change language without restarting the app

gui/kivy/i18n.py

@@ -0,0 +1,36 @@
+import gettext
+
+class _(str):
+
+    observers = set()
+    lang = None
+
+    def __new__(cls, s, *args, **kwargs):
+        if _.lang is None:
+            _.switch_lang('en')
+        t = _.translate(s, *args, **kwargs)
+        o = super(_, cls).__new__(cls, t)
+        o.source_text = s
+        return o
+
+    @staticmethod
+    def translate(s, *args, **kwargs):
+        return _.lang(s).format(args, kwargs)
+
+    @staticmethod
+    def bind(label):
+        if isinstance(label.text, _):
+            _.observers.add(label)
+
+    @staticmethod
+    def switch_lang(lang):
+        # get the right locales directory, and instanciate a gettext
+        from electrum.i18n import LOCALE_DIR
+        locales = gettext.translation('electrum', LOCALE_DIR, languages=[lang], fallback=True)
+        _.lang = locales.gettext
+        for label in _.observers:
+            try:
+                label.text = _(label.text.source_text)
+            except ReferenceError:
+                pass
+