fix: sometimes memories gets extracted in the wrong language

hindsight-api/hindsight_api/engine/retain/fact_extraction.py

@@ -441,7 +441,7 @@ def _chunk_conversation(turns: list[dict], max_chars: int) -> list[str]:
 # Concise extraction prompt (default) - selective, high-quality facts
 CONCISE_FACT_EXTRACTION_PROMPT = """Extract SIGNIFICANT facts from text. Be SELECTIVE - only extract facts worth remembering long-term.
 
-LANGUAGE RULE (CRITICAL): Output facts in the EXACT SAME language as the input text. If input is Japanese, output Japanese. If input is Chinese, output Chinese. NEVER translate to English. Preserve original language completely.
+LANGUAGE REQUIREMENT: Detect the language of the input text. All extracted facts, entity names, descriptions, and other output MUST be in the SAME language as the input. Do not translate to another language.
 
 {fact_types_instruction}
 

hindsight-api/tests/test_multilingual.py

@@ -275,6 +275,165 @@ async def test_retain_japanese_content(memory, request_context):
                 pass
 
 
+@pytest.mark.asyncio
+async def test_english_content_stays_english(memory, request_context):
+    """
+    Test that English content is NOT incorrectly translated to Japanese or Chinese.
+
+    This test specifically catches the bug where the language instruction in the
+    CONCISE extraction prompt mentioned Japanese/Chinese explicitly, which primed
+    the LLM to sometimes output facts in those languages even for English input.
+
+    See: https://github.com/vectorize-io/hindsight/issues/181
+    """
+    bank_id = f"test_english_retain_{datetime.now(timezone.utc).timestamp()}"
+
+    try:
+        # English content about a developer
+        english_content = """
+        John Smith is a software engineer at TechCorp in Seattle.
+        He specializes in machine learning and has been working on
+        recommendation systems for the past three years.
+        Last month, he launched a new feature that improved click-through rates by 25%.
+        He prefers working in Python and uses PyTorch for model training.
+        """
+
+        unit_ids = await memory.retain_async(
+            bank_id=bank_id,
+            content=english_content,
+            context="Team profile",
+            event_date=datetime(2024, 1, 15, tzinfo=timezone.utc),
+            request_context=request_context,
+        )
+
+        logger.info(f"Retained {len(unit_ids)} facts from English content")
+        assert len(unit_ids) > 0, "Should have extracted facts from English content"
+
+        # Recall with English query
+        result = await memory.recall_async(
+            bank_id=bank_id,
+            query="Tell me about John Smith",
+            budget=Budget.MID,
+            max_tokens=1000,
+            fact_type=["world"],
+            request_context=request_context,
+        )
+
+        assert len(result.results) > 0, "Should recall facts about John Smith"
+
+        # Verify facts are NOT in Japanese or Chinese
+        for fact in result.results:
+            logger.info(f"Fact: {fact.text}")
+
+            # Count Japanese characters (hiragana, katakana)
+            japanese_chars = sum(
+                1 for char in fact.text
+                if ("\u3040" <= char <= "\u309f") or ("\u30a0" <= char <= "\u30ff")
+            )
+
+            # Count Chinese/CJK characters (excluding those also used in Japanese)
+            # Note: Kanji/CJK ideographs overlap between Chinese and Japanese
+            cjk_chars = sum(1 for char in fact.text if "\u4e00" <= char <= "\u9fff")
+
+            # For English input, there should be minimal CJK characters
+            # Allow for occasional edge cases (e.g., proper nouns) but not full translation
+            total_chars = len(fact.text)
+            cjk_ratio = cjk_chars / max(total_chars, 1)
+
+            assert cjk_ratio < 0.1, (
+                f"English content was incorrectly translated to CJK language! "
+                f"CJK ratio: {cjk_ratio:.1%}, Japanese chars: {japanese_chars}, CJK chars: {cjk_chars}. "
+                f"Fact: {fact.text}"
+            )
+
+        logger.info("English content test passed - facts stayed in English")
+
+    finally:
+        await memory.delete_bank(bank_id, request_context=request_context)
+
+
+@pytest.mark.asyncio
+async def test_italian_content_stays_italian(memory, request_context):
+    """
+    Test that Italian content is NOT incorrectly translated to Japanese or Chinese.
+
+    Similar to the English test, this catches the bug where non-CJK languages
+    could be incorrectly translated due to biased language instruction.
+
+    See: https://github.com/vectorize-io/hindsight/issues/181
+    """
+    bank_id = f"test_italian_retain_{datetime.now(timezone.utc).timestamp()}"
+
+    try:
+        # Italian content about a chef
+        italian_content = """
+        Marco Rossi è uno chef italiano che lavora in un ristorante a Milano.
+        È specializzato nella cucina toscana e ha vinto tre premi gastronomici.
+        Il mese scorso ha aperto un nuovo ristorante nel centro della città.
+        Preferisce usare ingredienti freschi e locali per i suoi piatti.
+        """
+
+        unit_ids = await memory.retain_async(
+            bank_id=bank_id,
+            content=italian_content,
+            context="Profilo dello chef",
+            event_date=datetime(2024, 1, 15, tzinfo=timezone.utc),
+            request_context=request_context,
+        )
+
+        logger.info(f"Retained {len(unit_ids)} facts from Italian content")
+        assert len(unit_ids) > 0, "Should have extracted facts from Italian content"
+
+        # Recall with Italian query
+        result = await memory.recall_async(
+            bank_id=bank_id,
+            query="Dimmi di Marco Rossi",  # "Tell me about Marco Rossi"
+            budget=Budget.MID,
+            max_tokens=1000,
+            fact_type=["world"],
+            request_context=request_context,
+        )
+
+        assert len(result.results) > 0, "Should recall facts about Marco Rossi"
+
+        # Verify facts are NOT in Japanese or Chinese - should stay in Italian
+        for fact in result.results:
+            logger.info(f"Fact: {fact.text}")
+
+            # Count CJK characters
+            cjk_chars = sum(1 for char in fact.text if "\u4e00" <= char <= "\u9fff")
+            japanese_chars = sum(
+                1 for char in fact.text
+                if ("\u3040" <= char <= "\u309f") or ("\u30a0" <= char <= "\u30ff")
+            )
+
+            total_chars = len(fact.text)
+            cjk_ratio = (cjk_chars + japanese_chars) / max(total_chars, 1)
+
+            assert cjk_ratio < 0.1, (
+                f"Italian content was incorrectly translated to CJK language! "
+                f"CJK ratio: {cjk_ratio:.1%}. Fact: {fact.text}"
+            )
+
+        # Verify facts contain Italian words (basic sanity check)
+        all_text = " ".join(f.text for f in result.results).lower()
+        italian_indicators = ["marco", "rossi", "chef", "ristorante", "milano", "cucina", "italiano", "italiana"]
+        has_italian = any(word in all_text for word in italian_indicators)
+
+        # Allow English translation as acceptable (not ideal but not the bug)
+        english_indicators = ["chef", "restaurant", "milan", "italian", "cooking"]
+        has_english = any(word in all_text for word in english_indicators)
+
+        assert has_italian or has_english, (
+            f"Expected facts to be in Italian or English, but got neither. Facts: {all_text}"
+        )
+
+        logger.info("Italian content test passed - facts not translated to CJK")
+
+    finally:
+        await memory.delete_bank(bank_id, request_context=request_context)
+
+
 @pytest.mark.asyncio
 async def test_mixed_language_entities(memory, request_context):
     """