SpellCheck (5.1): Locale "text language" missing, but DE-frami extension installed!

[gloschtla]

Let’s look into /Tools/Options of LibreOffice 5.1.2.2 and then into language settings:
The language of user interface is English (USA).
The language of locale setting is German (DE).
In writing aids / available language modules i click on “edit” to see available languages: English (Canada, USA), Finnish, Indonesian, Irish …but no German!

Let’s look into /Tools/Extention manager:
German (DE-frami) spelling, hyphenation, thesaurus 2015.12.28 is installed.
So why is it not activated in the current version of Libre Office?

[gloschtla]

Here is the source of the extention DE-frami:
http://extensions.libreoffice.org/extension-center?getCategories=Dictionary