fix: doc_language return null when document segment settings (#7719)

api/controllers/console/datasets/datasets_document.py

                 "hit_count": document.hit_count,
                 "display_status": document.display_status,
                 "doc_form": document.doc_form,
+                "doc_language": document.doc_language,
             }
         else:
             process_rules = DatasetService.get_process_rules(dataset_id)
                 "hit_count": document.hit_count,
                 "display_status": document.display_status,
                 "doc_form": document.doc_form,
+                "doc_language": document.doc_language,
             }
 
         return response, 200

web/app/components/datasets/create/step-two/index.tsx

   const [docForm, setDocForm] = useState<DocForm | string>(
     (datasetId && documentDetail) ? documentDetail.doc_form : DocForm.TEXT,
   )
-  const [docLanguage, setDocLanguage] = useState<string>(locale !== LanguagesSupported[1] ? 'English' : 'Chinese')
+  const [docLanguage, setDocLanguage] = useState<string>(
+    (datasetId && documentDetail) ? documentDetail.doc_language : (locale !== LanguagesSupported[1] ? 'English' : 'Chinese'),
+  )
   const [QATipHide, setQATipHide] = useState(false)
   const [previewSwitched, setPreviewSwitched] = useState(false)
   const [showPreview, { setTrue: setShowPreview, setFalse: hidePreview }] = useBoolean()

web/models/datasets.ts

   completed_segments?: number
   total_segments?: number
   doc_form: 'text_model' | 'qa_model'
+  doc_language: string
 }
 
 export type SimpleDocumentDetail = InitialDocumentDetail & {