kivy i18n: test if label is already bound

gui/kivy/i18n.py

@@ -19,8 +19,7 @@ class _(str):
 
     @staticmethod
     def bind(label):
-        if isinstance(label.text, _):
-            _.observers.add(label)
+        _.observers.add(label)
 
     @staticmethod
     def switch_lang(lang):

gui/kivy/main.kv

@@ -12,7 +12,8 @@
     markup: True
     font_name: 'Roboto'
     font_size: '16sp'
-    on_text: _.bind(self)
+    bound: False
+    on_text: if isinstance(self.text, _) and not self.bound: self.bound = True; _.bind(self)
 
 <TextInput>
     on_focus: app._focused_widget = root