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, 6 insertions, 1 deletions

diff --git a/create/content_template_handler.go b/create/content_template_handler.go
index 705efbd20..e9e7cb62b 100644
--- a/create/content_template_handler.go
+++ b/create/content_template_handler.go
@@ -88,10 +88,15 @@ func executeArcheTypeAsTemplate(s *hugolib.Site, kind, targetPath, archetypeFile
 		err               error
 	)
 
-	sp := source.NewSourceSpec(s.Deps.Cfg, s.Deps.Fs)
+	ps, err := helpers.NewPathSpec(s.Deps.Fs, s.Deps.Cfg)
+	sp := source.NewSourceSpec(ps, ps.Fs.Source)
+	if err != nil {
+		return nil, err
+	}
 	f := sp.NewFileInfo("", targetPath, false, nil)
 
 	name := f.TranslationBaseName()
+
 	if name == "index" || name == "_index" {
 		// Page bundles; the directory name will hopefully have a better name.
 		dir := strings.TrimSuffix(f.Dir(), helpers.FilePathSeparator)