Fix: bad case for tokenizer. (#5543)

### What problem does this PR solve?

#5492

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

rag/nlp/rag_tokenizer.py

         self.stemmer = PorterStemmer()
         self.lemmatizer = WordNetLemmatizer()
 
-        self.SPLIT_CHAR = r"([ ,\.<>/?;:'\[\]\\`!@#$%^&*\(\)\{\}\|_+=《》，。？、；‘’：“”【】~！￥%……（）——-]+|[a-z\.-]+|[0-9,\.-]+)"
+        self.SPLIT_CHAR = r"([ ,\.<>/?;:'\[\]\\`!@#$%^&*\(\)\{\}\|_+=《》，。？、；‘’：“”【】~！￥%……（）——-]+|[a-zA-Z0-9,\.-]+)"
 
         trie_file_name = self.DIR_ + ".txt.trie"
         # check if trie file existence
     def english_normalize_(self, tks):
         return [self.stemmer.stem(self.lemmatizer.lemmatize(t)) if re.match(r"[a-zA-Z_-]+$", t) else t for t in tks]
 
+    def _split_by_lang(self, line):
+        txt_lang_pairs = []
+        arr = re.split(self.SPLIT_CHAR, line)
+        for a in arr:
+            if not a:
+                continue
+            s = 0
+            e = s + 1
+            zh = is_chinese(a[s])
+            while e < len(a):
+                _zh = is_chinese(a[e])
+                if _zh == zh:
+                    e += 1
+                    continue
+                txt_lang_pairs.append((a[s: e], zh))
+                s = e
+                e = s + 1
+                zh = _zh
+            if s >= len(a):
+                continue
+            txt_lang_pairs.append((a[s: e], zh))
+        return txt_lang_pairs
+
     def tokenize(self, line):
         line = re.sub(r"\W+", " ", line)
         line = self._strQ2B(line).lower()
         line = self._tradi2simp(line)
-        zh_num = len([1 for c in line if is_chinese(c)])
-        if zh_num == 0:
-            return " ".join([self.stemmer.stem(self.lemmatizer.lemmatize(t)) for t in word_tokenize(line)])
 
-        arr = re.split(self.SPLIT_CHAR, line)
+        arr = self._split_by_lang(line)
         res = []
-        for L in arr:
+        for L,lang in arr:
+            if not lang:
+                res.extend([self.stemmer.stem(self.lemmatizer.lemmatize(t)) for t in word_tokenize(L)])
+                continue
             if len(L) < 2 or re.match(
                     r"[a-z\.-]+$", L) or re.match(r"[0-9\.-]+$", L):
                 res.append(L)
                 continue
-            # print(L)
 
             # use maxforward for the first time
             tks, s = self.maxForward_(L)
                 self.dfs_("".join(tks[_j:]), 0, [], tkslist)
                 res.append(" ".join(self.sortTks_(tkslist)[0][0]))
 
-        res = " ".join(self.english_normalize_(res))
+        res = " ".join(res)
         logging.debug("[TKS] {}".format(self.merge_(res)))
         return self.merge_(res)