Yea, that doesn’t make sense. Why would Japan give a tax deduction for voluntarily paying into a foreign pension.
Do the UK give tax deductions to Japanese residing in UK, who voluntarily contribute to their Kokumin Nenkin?
I think the only occasion it might apply is if someone residing in japan is utilizing the elimination of dual coverage agreement in favour of the UK, meaning they have to pay UK, but then it wouldn’t be voluntary.