avoid split english in translation text

Former-commit-id: 4f07fba54f25dc645ed2998bfb24f0fc8060d04a

SRT.py

@@ -292,6 +292,12 @@ class SRT_script():
         else:
             trans_split_idx = len(translation) // 2
 
+            # to avoid split English word
+            for i in range(trans_split_idx, len(translation)):
+                if not translation[i].encode('utf-8').isalpha():
+                    trans_split_idx = i
+                    break
+
         # split the time duration based on text length
         time_split_ratio = trans_split_idx / (len(seg.translation) - 1)