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, 4 insertions, 0 deletions

diff --git a/helpers/url_test.go b/helpers/url_test.go
index 9572547c7..0ca3c8df2 100644
--- a/helpers/url_test.go
+++ b/helpers/url_test.go
@@ -27,6 +27,7 @@ import (
 func TestURLize(t *testing.T) {
 
 	v := viper.New()
+	v.Set("contentDir", "content")
 	l := NewDefaultLanguage(v)
 	p, _ := NewPathSpec(hugofs.NewMem(v), l)
 
@@ -88,6 +89,7 @@ func doTestAbsURL(t *testing.T, defaultInSubDir, addLanguage, multilingual bool,
 
 	for _, test := range tests {
 		v.Set("baseURL", test.baseURL)
+		v.Set("contentDir", "content")
 		l := NewLanguage(lang, v)
 		p, _ := NewPathSpec(hugofs.NewMem(v), l)
 
@@ -166,6 +168,7 @@ func doTestRelURL(t *testing.T, defaultInSubDir, addLanguage, multilingual bool,
 	for i, test := range tests {
 		v.Set("baseURL", test.baseURL)
 		v.Set("canonifyURLs", test.canonify)
+		v.Set("contentDir", "content")
 		l := NewLanguage(lang, v)
 		p, _ := NewPathSpec(hugofs.NewMem(v), l)
 
@@ -254,6 +257,7 @@ func TestURLPrep(t *testing.T) {
 	for i, d := range data {
 		v := viper.New()
 		v.Set("uglyURLs", d.ugly)
+		v.Set("contentDir", "content")
 		l := NewDefaultLanguage(v)
 		p, _ := NewPathSpec(hugofs.NewMem(v), l)