For example, if the frontmatter of a document is:

```
---
title: "This is a title"
---
```

Then it will render as "This is a title" as expected. However, if it is:

```
---
title: strings.page_one.heading
---
```

Then it will look for the file in `_data/strings.json` for the following
entry:

```
{
  "page_one": {
    "heading": "This is a heading",
    ...
  },
  ...
}
```

and the resulting heading will be "This is a heading". If the resulting
JSON entry cannot be found, it is presumed that it is not actually
trying to i18n the title and will instead use whatever it found in the
frontmatter (e.g. "not.json" will result in a title of "not.json").

The rationale for this is that the polyglot plugin doesn't support i189n
titles, because they rightly point out that you can [do this kind of
string lookup quite trivially in a liquid
template](https://github.com/untra/polyglot/issues/34#issuecomment-252774718).
However, that doesn't take into account the fact that page titles appear
elsewhere, such as in pagination pages. This would require the same
logic to appear everywhere a document title could be rendered.

Additionally, we already have a process for translating
post/documentation page titles, where the title is translated in weblate
right next to the document content. It would be annoying to say the
least if people translated documents in the "Docs" weblate project (a
.po based project), but then had to go to a different (JSON based)
project in order to translate the titles.