Localize date mask in lessons

The default date format looks a bit odd and is sometimes harder to read when carried over to Japanese.

I suggest implementing something like this:

Hopefully this will be possible to implement without messing up the date formatting for the other languages.

@imasaru What is the date formatting string would be for this?

Something like yy.MM.dd, at least. If you want to preserve the style that you used with English, you can omit the year like I did in the second photo above.

In that photo, I tried to preserve the day, month, and year as much as possible, creating: MM月.dd日 (EEE)

We have to localize the date mask, so it will be good for any language.