Translate en.json in ja [Manual Sync] (#1296)

Sync of partially translated files: 
untranslated content is included with source language content.

Co-authored-by: transifex-integration[bot] <43880903+transifex-integration[bot]@users.noreply.github.com>
Co-authored-by: Anna Iosif <anna.iosif@me.com>