Back in 2009, in topic #2971, the English name for the franchise Yamamura Sadako originates from was chosen, that being The Ring (since it's less ambiguous than just ring, and not as silly as its alias of Ringu). While the differences between the Japanese and American movies was brought up, it was still decided to have one united copyright tag (and in the years since we still do not have an active set of copytags based on the follow-up movies on either end).
In that entire time though, the franchise Saeki Kayako originates from has seemingly been ignored. Both the Japanese and English names for the franchise, Ju-on and The Grudge, are active copytags with seemingly no difference between the two. Both tags were created at the same time for post #14397, each tag's wikis were made at the same time earlier this year, and the only distinction between the two looks to be just what title the tagger remembered at that moment (not to mention all the overlap). So it's about time we finally resolve this, but the only question is what name to go with.
Based on the Ring, it might make sense to go with the English title, but what made that decision easy for the Ring was the fact that the Japanese title was just "Ring" in Japanese, while the original Japanese title for the Grudge wasn't a loanword, being 呪怨. Additionally, with so many years in the record, we can see that the last couple of instances where the Grudge was tagged were Ring mistags (i.e. tagging the Grudge with Sadako), with Ju-on not having this issue (instead having a handful of posts where Kayako was confused for Sadako, copytags included). So, I'll offer both options as BURs.