Translation:They are talking about the new school rule.
Would it also be correct without the "tentang"?
Thank you for bringing this up.
The ID sentence is actually incorrect.
'tentang' cannot be used here in combination with 'membicarakan'.
'membicarakan' = 'berbicara tentang' = to talk about.
-1) 'Mereka berbicara tentang peraturan.'
-2) 'Mereka membicarakan peraturan.'
Sentence 1) uses an intransitive verb (berbicara) and here you have to use 'tentang'.
Sentence 2) uses a transitive verb, this verb cannot use 'tentang' before the object.