[demo] support English

app.py

@@ -31,6 +31,7 @@ def recognition(audio, lang='CN'):
     # NOTE: model supports 16k sample_rate
     y = (y * (1 << 15)).astype("int16")
     global cur_lang
+    global decoder
     if lang == 'CN':
         if cur_lang != lang:
             del decoder