How do you verify foreign workers' understanding of safety training?

Hello. I am in charge of safety training at a manufacturing workplace where foreign workers are employed.
Currently, we provide Korean training materials along with translated summaries to new hires and those changing duties. While foremen capable of interpreting re-explain the key points and obtain signatures for the training, it is difficult to verify whether they actually understand the criteria for stopping work or the reporting procedure for equipment malfunctions.
We are considering using picture cards or task demonstrations, as conducting simple tests can feel like evaluating language skills, and receiving only confirmation of "understood" might cause important details to be missed. In particular, we plan to designate separate categories for items that require verification through actions, such as wearing protective gear, checking locks, and performing emergency stops and evacuations.
How is it appropriate to verify foreign workers' understanding of safety training? I am also curious about the extent to which interpreter explanations, workers' work demonstrations, picture-based verification questions, and retraining results are recorded in the training log.