* Fix i18n not working after 277d5a7
The translation strings file in "core" package should have file names
"core-strings.json" or "core-jsdoc-strings.json".
* Enable ja translation
Rename "core-strings.json" to "core-jsdoc-strings.json".
Add new "core-strings.json" as a copy of the template.
Add two lines for the files in "pxt.json".
0b469f69b6