Translation System

[wodka]

Since it is not possible in the original slate slatedocs/slate#445

Let's build something similar to this:

index.html.md
index.de.html.md

with includes that fall back to a default:

inclues/_first.html
inclues/_first.de.html

includes/_second.html

the generated files would then look like:

/ -> /index.html
/de -> /de/index.html

new in config block:

language: en
languages:
  - en
  - de