how to add language to zextras docs server

Hi, I'm from Japan.I has constructed a ZCS server and another server-which is Zextras Docs.

I was happy to see documents and spreadsheet through browser.

But I cannot select a language-Japanese via LibreOffice tool menu.

Italy Holland Spain German France Russia England and US are listed up.

I cannot find Japanese, but I can select only font, for example Noto Sans JP and so...

My system-both ZCS and Zextras Docs Server's locale setting is Ja_JP.UTF-8

After confirming locale setting, I had installed Zextras Zimbra9OSE and Zextras Docs.

Please teach me how to add Japanese Language to LibreOffice's settings and menu.

and tell me how to configure server settings.

Regards.