You can use APEX_LANG API to translate messages.

• APPLY_XLIFF_DOCUMENT Procedure
  
• CREATE_LANGUAGE_MAPPING Procedure
  
• CREATE_MESSAGE Procedure
  
• DELETE_LANGUAGE_MAPPING Procedure
  
• DELETE_MESSAGE Procedure
  
• EMIT_LANGUAGE_SELECTOR_LIST Procedure
  
• GET_LANGUAGE_SELECTOR_LIST Function
  
• GET_MESSAGE Function
  
• GET_XLIFF_DOCUMENT Function
  
• LANG Function
  
• MESSAGE Function (Deprecated)
  
• PUBLISH_APPLICATION Procedure
  
• SEED_TRANSLATIONS Procedure
  
• UPDATE_LANGUAGE_MAPPING Procedure
  
• UPDATE_MESSAGE Procedure Signature 1
  
• UPDATE_MESSAGE Procedure Signature 2
  
• UPDATE_TRANSLATED_STRING Procedure