Localize markdown-it-container

[Martien]

Behaviour like in the live demo at css-class-warning-lang-nl, using markdown-it-container like so:

::: warning
*here be dragons*
:::

results in:

<div class="warning">
  <em>here be dragons</em>
</div>

Likewise, it would be nice if:

::: warning lang=nl
*hier zijn draken*
:::

and joined at the hip with the proper css:

.warning::before {
    content: "Warning: ";
    color: red;
    font-weight: bold;
}
.warning:lang(nl)::before {
    content: "Pas op! ";
}

results in:

<div class="warning" lang="nl">
  <em>here be dragons</em>
</div>

and its rendering:

Pas op! hier zijn draken

In fact, everything that follows the class name can be copied as is into the corresponding <div> declaration.