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

2 files changed, 2 insertions, 1 deletions

diff --git a/i18n/i18n_test.go b/i18n/i18n_test.go
index 057fc35e9..4f5b3fbac 100644
--- a/i18n/i18n_test.go
+++ b/i18n/i18n_test.go
@@ -200,6 +200,7 @@ func TestI18nTranslate(t *testing.T) {
 	var actual, expected string
 	v := viper.New()
 	v.SetDefault("defaultContentLanguage", "en")
+	v.Set("contentDir", "content")
 
 	// Test without and with placeholders
 	for _, enablePlaceholders := range []bool{false, true} {
diff --git a/i18n/translationProvider.go b/i18n/translationProvider.go
index 52aada8bd..fa5664210 100644
--- a/i18n/translationProvider.go
+++ b/i18n/translationProvider.go
@@ -39,7 +39,7 @@ func NewTranslationProvider() *TranslationProvider {
 // Update updates the i18n func in the provided Deps.
 func (tp *TranslationProvider) Update(d *deps.Deps) error {
 	dir := d.PathSpec.AbsPathify(d.Cfg.GetString("i18nDir"))
-	sp := source.NewSourceSpec(d.Cfg, d.Fs)
+	sp := source.NewSourceSpec(d.PathSpec, d.Fs.Source)
 	sources := []source.Input{sp.NewFilesystem(dir)}
 
 	themeI18nDir, err := d.PathSpec.GetThemeI18nDirPath()