feat: add multilingual mode support (#241)

BREAKING CHANGE:  Layout file renamed ´layouts/partials/page-footer.html → layouts/partials/menu-nextprev.html`. If you use overrides, you might need to change the filenames as well.

exampleSite/content/en/shortcodes/mermaid.md

@@ -0,0 +1,46 @@
+---
+title: Mermaid
+---
+
+[Mermaid](https://mermaidjs.github.io/) is library for generating SVG charts and diagrams from text.
+
+## Example
+
+{{< columns >}}
+
+<!-- prettier-ignore -->
+```tpl
+{{</* mermaid class="text-center"*/>}}
+sequenceDiagram
+    Alice->>Bob: Hello Bob, how are you?
+    alt is sick
+        Bob->>Alice: Not so good :(
+    else is well
+        Bob->>Alice: Feeling fresh like a daisy
+    end
+    opt Extra response
+        Bob->>Alice: Thanks for asking
+    end
+{{</* /mermaid */>}}
+```
+
+<--->
+
+<!-- spellchecker-disable -->
+<!-- prettier-ignore -->
+{{< mermaid class="text-center" >}}
+sequenceDiagram
+    Alice->>Bob: Hello Bob, how are you?
+    alt is sick
+        Bob->>Alice: Not so good :(
+    else is well
+        Bob->>Alice: Feeling fresh like a daisy
+    end
+    opt Extra response
+        Bob->>Alice: Thanks for asking
+    end
+{{< /mermaid >}}
+
+<!-- spellchecker-enable -->
+
+{{< /columns >}}