I'm sorry to hear about your editing issues with Japanese text. The bug you've referenced is applicable to Jive 6.0.2, but our engineering team was unable to reproduce the issue. Specifically, the details are:
When Enter is pressed to finalize the first string, the whole string moves to the second line on its own, and the cursor moves to the beginning of the second line. Any text entered from that point gets entered from the cursor position. The user is able to move the cursor around to the correct position, but this is not ideal.
Depending on which version you're on, this may not be applicable either. Testing against the latest version of Jive 8 and Jive Cloud, I not seeing double cursors in Safari or Chrome when editing with Japanese characters. Since this will likely require targeted troubleshooting for your specific environment, I'd recommend submitting a support case in your private Jive Community customer group for further investigation. If you're not familiar with the case submission process, please work with your community manager to identify your submission process. In the support case, please provide specific steps to reproduce the issue, screenshots of what you're seeing, and a sample of the text or code you're entering.
Let me know if you had any other questions on this.