There is an Oxford learner's dictionary for people not fluent in English.
From the economist.com
The first Advanced learner's dictionary was the Oxford Advanced Learner's Dictionary, first published 63 years ago.
From the en.wikipedia.org
And while the definitions in standard dictionaries are often written in difficult language, those in a monolingual learner's dictionary aim to be simple and accessible.
From the en.wikipedia.org
A learner's comprehensive dictionary of Indonesian.