diff --git a/backend/app/services/ontology_generator.py b/backend/app/services/ontology_generator.py
index 316eb23..0601f3a 100644
--- a/backend/app/services/ontology_generator.py
+++ b/backend/app/services/ontology_generator.py
@@ -189,7 +189,8 @@ class OntologyGenerator:
             additional_context
         )
         
-        system_prompt = f"{ONTOLOGY_SYSTEM_PROMPT}\n\n{get_language_instruction()}"
+        lang_instruction = get_language_instruction()
+        system_prompt = f"{ONTOLOGY_SYSTEM_PROMPT}\n\n{lang_instruction}\nIMPORTANT: Entity type names MUST be in English PascalCase (e.g., 'PersonEntity', 'MediaOrganization'). Relationship type names MUST be in English UPPER_SNAKE_CASE (e.g., 'WORKS_FOR'). Attribute names MUST be in English snake_case. Only description fields and analysis_summary should use the specified language above."
         messages = [
             {"role": "system", "content": system_prompt},
             {"role": "user", "content": user_message}