Most modern English learner's dictionaries use controlled defining vocabulary for defining lemmas. Which German learner's dictionaries incorporate controlled defining vocabulary?
There are a few German dictionaries for learners that use a more restricted vocabulary than dictionaries for (adult) native speakers:
- Duden - Basiswörterbuch Deutsch als Fremdsprache: according to the description on the Duden website, the definitions in this dictionary use only words that are defined in the dictionary, apparently 7.000 words. It contains the entire vocabulary for the Goethe-Zertifikat B1 (but not only those, I think). The current edition dates from 2013.
- Duden - Deutsch als Fremdsprache - Standardwörterbuch: this dictionary has 20.000 entries and is geared at learners on the levels B1 - C1. According to the publisher's description, the definitions are "easy to understand", but this is not defined in terms of controlled vocabulary. The current edition dates from 2018.
- Langenscheidt Großwörterbuch Deutsch als Fremdsprache is probably a "classic" in this field, as it has been around since the early 1990s. It is aimed at learners and contains 90.000 definitions, phrases and example sentences. Unfortunately, neither the publisher's website nor the dictionary's introduction mention the use of a controlled vocabulary (even though the definitions are simpler than what you find in dictionaries for native speakers).
- PONS Großwörterbuch Deutsch als Fremdsprache contains 110.000 definitions, phrases and example sentences. However, neither the publisher's website nor the dictionary's introduction mention the use of a controlled vocabulary.
Based on this brief overview, the only learner's dictionary of which I can confidently say that it uses a controlled vocabulary for its definitions is Duden - Basiswörterbuch Deutsch als Fremdsprache. For the other dictionaries, I can only assume that they use a controlled vocabulary.
Update August 2020: Online, there is Online-Wörterbuch Deutsch als Fremdsprache von PONS, which is presumably based on the printed version (or the other way around).
I do not know if and to what extent "controlled defining vocabulary" is an issue in German monolingual dictionaries in terms of a concept that is explicitely defined as a policy, i.e. beyond the natural use of more simple and frequent words to describe the meaning of more complex or rare ones.
For yourself to assess, here is a page taken from "Duden Deutsches Universalwörterbuch", 8th edition. This dictionary is not intended explicitely for the use of learners with other first language, though, rather it is meant for universal use.
(I skimmed through the variuos prefaces of this 2000 pages dictionaries, but I did not find something like "controlled dictionary" mentioned there.)
One observation however: reading definitions like
Abfalleimer: Eimer für den Abfall
it seems to me that the concept of "controlled defining dictionary" is used here (although perhaps involuntarily), as you could argue that for a native speaker of German you do not need a simple-worded definition like "Eimer für den Abfall" for a word like "Abfalleimer" that a) everybody 3 years old knows and b) that is self-explanatory.
My recommendation is Pons Großwörterbuch Deutsch als Fremdsprache, see Pons Shop, which would exactly address, what you look for, but I'm unsure concerning the size of vocabulary used for explanations. For Abfalleimer there is just a reference to Mülleimer, which in turn is defined as
Behälter für den Hausmüll
Stoffe, die nicht mehr verwendet und deshalb beseitigt werden