Creating vocabulary training with dialog cards are a longtime wish from users of Moodle. There are several third party plugins like flash cards that offer a similar feature. The most advanced feature are Dialog Cards from H5P plugin. In the latest version its possible to repeat cards that are not answered correct in a second and third round.
Its very helpfull in language training but also for lots of other topics.
There is one missing feature in this plugin that we can close now easily. In the moment its not possible to save the status and restart hours or days later in this status: spaced repetition.
I met OliverTacke in Hamburg two weeks ago. He is a software developer working with Moodle and the H5P team in Norway for a long time now. He started an Indiegogo campaign to fix this issue. https://www.indiegogo.com/projects/unlock-spaced-repetition-for-h5p-dialog-cards#/
The software code is ready for use, but finally he needs some money that the H5P company Joubel will integrate it into core code.
The campaign is running for 11 more days. Actual 2/3 are funded. 500 € more are required to finish this project.
I would like to see this project funded. You can start with 5 or 10 €/$, but any amount is helpfull.
PS: Moodle Roadmap describes that its planned to improve the H5P plugin for Moodle 3.8 (November 2019). There is also a discussion to add the plugin into core.