Multi lingual i18n file

I try to use the i18n/at-de.yaml in root dir or in the theme dir of my site as described in https://gohugo.io/content/multilingual/

The file looks pretty simple

- id: wordcount
  translation: "Diese Seite hat {{ .WordCount }} Wörter."

That’s it.
the config.toml looks like this.

defaultContentLanguage = "at-DE"
languageCode = "at-DE"
title = "Acme"
baseurl = "http://acme.com/"
theme = "mytheme"
author = "Aleks"
copyright = "Copyright (c) 2016 - 2017, Aleks; all rights reserved."
canonifyurls = true
#paginate = 5

# disqusShortname = "xxxxxx"
googleAnalytics = "xxxx"

[Languages]
[Languages.at-de]
copyright = "Copyright (c) 2016 - 2017, Aleks; Alle rechte vorbehalten"

[Languages.en]
copyright = "Copyright (c) 2016 - 2017, Aleks; all rights reserved."

the error is

 ~/Downloads/hugos/hugo_0.18_linux_amd64/hugo_0.18_linux_amd64 --buildDrafts -v --i18n-warnings
INFO: 2016/12/30 01:22:30 hugo.go:349: Using config file: /bigdisk01/al/work/testsite001/testsite003/config.toml
INFO: 2016/12/30 01:22:30 hugo.go:497: using a UnionFS for static directory comprised of:
INFO: 2016/12/30 01:22:30 hugo.go:498: Base: /bigdisk01/al/work/testsite001/testsite003/themes/mytheme/static
INFO: 2016/12/30 01:22:30 hugo.go:499: Overlay: /bigdisk01/al/work/testsite001/testsite003/static/
INFO: 2016/12/30 01:22:30 hugo.go:532: syncing static files to /bigdisk01/al/work/testsite001/testsite003/public/
Started building sites ...
Error: Error building site: Failed to read data from translations/at-DE.yaml/at-DE.yaml: yaml: unmarshal errors:

Try with Hugo v0.18.1 bugfix release. You should see the end of that error message now.