Clarify what JSON-LD does and doesn't do

[r12a]

3.1.3.2 Create a new datatype in JSON-LD
https://w3c.github.io/string-meta/#langapproach2

I think this section should start by saying that JSON-LD does something similar already, but only for language. Then show the example as JSON-LD, ie. without the dir stuff.

Then add the explanation of why this doesn't always work.

Then make the point that it doesn't support dir, which may look like <show current version of the example>.

But the focus of this section is really language, so this should really just be entre parenthèses.

[aphillips]

Actually, JSON-LD doesn't really do what this section discusses. It provides two things: the ability to add an @language item to a given context (which would be a mechanism for setting a whole document to that language). It also provides the language map feature, which we use in the best practices for localization bits. But it doesn't provide an internationalized string type, which is what this section is talking about. In practice, JSON-LD may be the wrong thing to call out here probably. What is wanted is a low-level type in JSON itself.