print warning when add-ons access _ without importing it

aqt/__init__.py

@@ -137,8 +137,11 @@ def setupLang(pm, app, force=None):
     # gettext
     _gtrans = gettext.translation(
         'anki', dir, languages=[lang], fallback=True)
-    builtins.__dict__['_'] = _gtrans.gettext
-    builtins.__dict__['ngettext'] = _gtrans.ngettext
+    def fn(*args):
+        print("accessing _ and ngettext without importing from anki.lang will break in the future")
+        print("".join(traceback.format_stack()[-2]))
+    builtins.__dict__['_'] = fn
+    builtins.__dict__['ngettext'] = fn
     anki.lang.setLang(lang, local=False)
     if lang in ("he","ar","fa"):
         app.setLayoutDirection(Qt.RightToLeft)

aqt/profiles.py

@@ -357,10 +357,6 @@ please see:
     # On first run, allow the user to choose the default language
 
     def _setDefaultLang(self):
-        # the dialog expects _ to be defined, but we're running before
-        # setupLang() has been called. so we create a dummy op for now
-        import builtins
-        builtins.__dict__['_'] = lambda x: x
         # create dialog
         class NoCloseDiag(QDialog):
             def reject(self):