Hi everyone, first of all let me say I really like what you've done here and the fact that you've let us beta test this site.
I've incorporated Lingvist into my daily language learning routine and it's really working out for me nicely. Beside my Duolingo tasks, here I do two languages at a time, 200 cards for the primary language and 100 secondary, and also read Wikipedia and listen to radio. Now I'm glad to say I've "graduated" in Spanish here and waiting for more words, plan to just clear the stack every few days, and now my new primary language is the former secondary (German) while the new secondary is French.
But anyway enough of that intro, let me reconnect to what I said about graduating the Spanish course, I really didn't like how the site responds when the stack ends. Not when a user graduates, that notification message is fine. But whenever I clear a repeat stack beyond that graduation milestone, after completing the last card successfully, the lights just go green, there is not even sound for reading that sentence and it seems the site freezes (granted that I finished the course only yesterday, but since after that I finished a repeat stack a couple of times, and today once, and since both times it happened I'm inclined to think it's just how the site handles the stack end). Yesterday I even restarted Firefox and redid the stacks cause I felt it was something on my end, and had a similar feeling today.
So I suggest at the end just adding a message or something like "You've finished the stack for the day, come back tomorrow" etc, idk.