make highlight friendly to English (#2417)

### What problem does this PR solve?

#2415

### Type of change

- [x] Performance Improvement

rag/nlp/__init__.py

@@ -214,7 +214,7 @@ def is_english(texts):
     eng = 0
     if not texts: return False
     for t in texts:
-        if re.match(r"[a-zA-Z]{2,}", t.strip()):
+        if re.match(r"[ `a-zA-Z.,':;/\"?<>!\(\)-]", t.strip()):
             eng += 1
     if eng / len(texts) > 0.8:
         return True