I think "berulang" is more precise than "sering"
"Sering" must be translated as "often"
"berulang" doesn't always means "frequent", something that happen monthly can be called "berulang." well, "berulang tahun" means "having a birthday", and birthday is never frequent. :)
IMO, the translation is precise.
Apa bedanya sama ,often?
Often = kata keterangan. I see him often.
Frequent = kata sifat. It's frequent.
Kenapa nggak frequence? Kan sama aja
Tidak. Frequent = kata sifat. Dan Frequence = kata benda.