Refa: remove dataset language and validate dataset name length. (#5707)

### What problem does this PR solve?

#5686
#5702

### Type of change

- [x] Refactoring

sdk/python/ragflow_sdk/modules/dataset.py

@@ -30,7 +30,6 @@ class DataSet(Base):
         self.avatar = ""
         self.tenant_id = None
         self.description = ""
-        self.language = "English"
         self.embedding_model = ""
         self.permission = "me"
         self.document_count = 0