ruby.lua should not set lang=ja

[ctrlcctrlv]

It seems strange that ruby.lua does this:

sile/packages/ruby.lua

Line 2 in e5ee467

SILE.call("language", { main = "ja" }, {})

I can't think of a legitimate reason to. Even if we assume ruby is only used for 振り仮名^🐣 (it isn't!), they already should be using a Japanese class, right?

But ruby is often also used for pinyin, bopomofo, etc:

[alerque]

Sounds reasonable to me, but out of my depth to confirm.

[simoncozens]

OK, I see why it calls that - the idea was to do \language[main=ja]{}, loading up Japanese language support to get access to the "zw" (全角 width) unit, but scoping the change of language to the empty block. (Similar to \font[...]{foo} versus \font[..] foo. But it doesn't quite work. I'll fix it.

[alerque]

If the zw unit is useful across more that just Japanese, perhaps it should be moved somewhere higher up than the language support code?

[simoncozens]

In theory, maybe? In practice, while there is an extremely useful W3C specification for handling Japanese text, there's not a similar one for handling Chinese text, so I'm not currently in a position to support Chinese typesetting in the same way. If we do have something to share, we'll share it, but not yet.