Thanks in advance for your help.
7 answers
Finally Salesforce Support came back to me with some solid feedback:
Topic Detail Page as a dynamic page that cannot be translated as it is currently working as designed and have no other workaround to translate it as of the moment.
We understand that the documentation you've found didn't specifically indicate that translating the Topic Detail Page is currently a limitation so rest assured that we'll reach out to our internal team to update the said documentation to reflect the appropriate information needed.