Can entries be disabled by default for 2/3 of the languages on my website
Is it possible to have the Japanese and English version disabled by default?


Yes. Visit Settings -> Sections -> [Your Section Name] inside the Control Panel.

Under the heading Which locales should entries in this section target? there's a Default Entry Status Lightswitch for each locale. Make sure the Lightswitches are off (i.e., not green) for the English and Japanese locales, and you're all set.

Obviously, you'll need to do this for any and all sections targeting the 3 locales – there's no "global" setting for it.