diff --git a/rag/nlp/__init__.py b/rag/nlp/__init__.py
index b6a02f2713..9e7f332dbd 100644
--- a/rag/nlp/__init__.py
+++ b/rag/nlp/__init__.py
@@ -237,7 +237,7 @@ def is_english(texts):
     if not texts:
         return False
 
-    pattern = re.compile(r"[`a-zA-Z0-9\s.,':;/\"?<>!\(\)\-]")
+    pattern = re.compile(r"[`a-zA-Z0-9\s.,':;/\"?<>!\(\)\-]+")
 
     if isinstance(texts, str):
         texts = list(texts)
diff --git a/test/unit_test/rag/test_is_english.py b/test/unit_test/rag/test_is_english.py
new file mode 100644
index 0000000000..3b589065f6
--- /dev/null
+++ b/test/unit_test/rag/test_is_english.py
@@ -0,0 +1,60 @@
+#
+#  Copyright 2025 The InfiniFlow Authors. All Rights Reserved.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+
+import sys
+import types
+
+import pytest
+
+
+def _stub(name, **attrs):
+    mod = types.ModuleType(name)
+    for key, value in attrs.items():
+        setattr(mod, key, value)
+    sys.modules.setdefault(name, mod)
+    return mod
+
+
+# Stub heavy module-level imports so rag.nlp can be imported in isolation.
+_stub("common.token_utils", num_tokens_from_string=lambda *a, **k: 0)
+_stub("roman_numbers")
+_stub("word2number", w2n=types.SimpleNamespace())
+_stub("cn2an", cn2an=lambda *a, **k: 0)
+_pil = _stub("PIL")
+_pil.Image = _stub("PIL.Image")
+_stub("chardet")
+
+from rag.nlp import is_english
+
+
+@pytest.mark.p2
+def test_is_english_string_path_unchanged():
+    assert is_english("This is English") is True
+
+
+@pytest.mark.p2
+def test_is_english_list_of_english_sentences():
+    assert is_english(["The quick brown fox jumps.", "Hello world today.", "Good morning sir."]) is True
+
+
+@pytest.mark.p2
+def test_is_english_single_english_answer_in_list():
+    assert is_english(["This is a normal English answer."]) is True
+
+
+@pytest.mark.p2
+def test_is_english_chinese_list_is_false():
+    assert is_english(["这是中文段落。", "另一个中文段落。"]) is False