add local_ja

[taisukef]

Thank you for the great project!

[pfalstad]

Thank you! I put this on my site, see it here: https://www.falstad.com/circuit/circuitjs.html?lang=ja

Though it won't show up in the options menu yet, I'll get around to that later.

[taisukef]

Thank you!

The application defaults to the browser settings, so Japanese language is already displayed for Japanese users.

[taisukef]

We've added and improved Japanese translations.

[pfalstad]

Thanks, I've updated my site