Add support for a content dir set per language

A sample config:

```toml
defaultContentLanguage = "en"
defaultContentLanguageInSubdir = true

[Languages]
[Languages.en]
weight = 10
title = "In English"
languageName = "English"
contentDir = "content/english"

[Languages.nn]
weight = 20
title = "På Norsk"
languageName = "Norsk"
contentDir = "content/norwegian"
```

The value of `contentDir` can be any valid path, even absolute path references. The only restriction is that the content dirs cannot overlap.

The content files will be assigned a language by

1. The placement: `content/norwegian/post/my-post.md` will be read as Norwegian content.
2. The filename: `content/english/post/my-post.nn.md` will be read as Norwegian even if it lives in the English content folder.

The content directories will be merged into a big virtual filesystem with one simple rule: The most specific language file will win.
This means that if both `content/norwegian/post/my-post.md` and `content/english/post/my-post.nn.md` exists, they will be considered duplicates and the version inside `content/norwegian` will win.

Note that translations will be automatically assigned by Hugo by the content file's relative placement, so `content/norwegian/post/my-post.md` will be a translation of `content/english/post/my-post.md`.

If this does not work for you, you can connect the translations together by setting a `translationKey` in the content files' front matter.

Fixes #4523
Fixes #4552
Fixes #4553

1 files changed, 7 insertions, 1 deletions

diff --git a/tpl/collections/collections_test.go b/tpl/collections/collections_test.go
index f35e29459..68e7c59d6 100644
--- a/tpl/collections/collections_test.go
+++ b/tpl/collections/collections_test.go
@@ -369,7 +369,7 @@ func TestIntersect(t *testing.T) {
 func TestIsSet(t *testing.T) {
 	t.Parallel()
 
-	ns := New(newDeps(viper.New()))
+	ns := newTestNs()
 
 	for i, test := range []struct {
 		a      interface{}
@@ -787,3 +787,9 @@ func newDeps(cfg config.Provider) *deps.Deps {
 		Log:         jww.NewNotepad(jww.LevelError, jww.LevelError, os.Stdout, ioutil.Discard, "", log.Ldate|log.Ltime),
 	}
 }
+
+func newTestNs() *Namespace {
+	v := viper.New()
+	v.Set("contentDir", "content")
+	return New(newDeps(v))
+}