teaching all verb forms
When I click on the conjugate table there are often many forms I've never seen, especially for the harder verbs (e.g. erwerben, leisten... in German)
I've noticed Duolingo get better at showing a few more of the present 'indicative' forms but they should make sure for each verb they've got three or more sentences for each form, including all of the 'conditional' and 'other' forms (there may be other special forms for other languages).
I think doing this would make it easier to learn the trickier tenses while also helping me memorise verbs without seeing them in just one form over and over.