[core] Improve error reporting for entity name conflicts with non-ASCII characters

esphome/core/entity_helpers.py

@@ -236,10 +236,20 @@ def entity_duplicate_validator(platform: str) -> Callable[[ConfigType], ConfigTy
             if existing_component != "unknown":
                 conflict_msg += f" from component '{existing_component}'"
 
+            # Show both original names and their ASCII-only versions if they differ
+            sanitized_msg = ""
+            if entity_name != name_key or existing_name != name_key:
+                sanitized_msg = (
+                    f"\n  Original names: '{entity_name}' and '{existing_name}'"
+                    f"\n  Both convert to ASCII ID: '{name_key}'"
+                    f"\n  To fix: Add unique ASCII characters (e.g., '1', '2', or 'A', 'B') to distinguish them"
+                )
+
             raise cv.Invalid(
                 f"Duplicate {platform} entity with name '{entity_name}' found{device_prefix}. "
                 f"{conflict_msg}. "
                 f"Each entity on a device must have a unique name within its platform."
+                f"{sanitized_msg}"
             )
 
         # Store metadata about this entity

tests/unit_tests/core/test_entity_helpers.py

@@ -705,3 +705,28 @@ def test_empty_or_null_device_id_on_entity() -> None:
     config2 = {CONF_NAME: "Temperature", CONF_DEVICE_ID: None}
     validated2 = validator(config2)
     assert validated2 == config2
+
+
+def test_entity_duplicate_validator_non_ascii_names() -> None:
+    """Test that non-ASCII names show helpful error messages."""
+    # Create validator for binary_sensor platform
+    validator = entity_duplicate_validator("binary_sensor")
+
+    # First Russian sensor should pass
+    config1 = {CONF_NAME: "Датчик открытия основного крана"}
+    validated1 = validator(config1)
+    assert validated1 == config1
+
+    # Second Russian sensor with different text but same ASCII conversion should fail
+    config2 = {CONF_NAME: "Датчик закрытия основного крана"}
+    with pytest.raises(
+        Invalid,
+        match=re.compile(
+            r"Duplicate binary_sensor entity with name 'Датчик закрытия основного крана' found.*"
+            r"Original names: 'Датчик закрытия основного крана' and 'Датчик открытия основного крана'.*"
+            r"Both convert to ASCII ID: '_______________________________'.*"
+            r"To fix: Add unique ASCII characters \(e\.g\., '1', '2', or 'A', 'B'\)",
+            re.DOTALL,
+        ),
+    ):
+        validator(config2)