More different words in strengthen exercises
It is often mentioned in the discussions that some words are four times presented in one strengthen exercise, also when the first time the word is correct translated. Maybe that's because all the sentences are selected when starting the exercise and DL doesn't change the selected sentences when a word is the first time correct translated.
DL takes maximum 7, maybe 10 new words, for an exercise. For strengthen exercises it should be possible to choose the number of words presented in the exercise (for example: one (new or to test) word per sentence.
It should also be possible to choose one direction, for example: only translation in the language to learn. There are user written extensions for this purpose, but with the maximum of 7 or 10 new words, you get always the same words.
edit: with the 7 or 10 words each exercises, you need three strengthen exercises for bringing a skill from 1/5 to 5/5 for well know skills. For a well know skill should it be possible with one exercise of 20 sentences, with 20 words.