Probably a bug : "You have practiced all of your words. Try doing some lessons or translations."
I kinda have a bug lately ... I seem to have dozens of skills that are not golden, but i get this when i go to strengthen your skills I mostly get "You have practiced all of your words. Try doing some lessons or translations." ... even after like 2-3 days of not learning anything, I just get like only one strengthen lesson after which i get the message again (and i still have lots and lots of not-fully-trained lessons). Thanks for any future help.
I'm afraid it's not... There have been many complaints in the forum about this, I think it has to do with the XP reduction for reviewed skills.
It seems that Duolingo is try to force us learning new stuff instead of practicing things we believe we do not master. I think they should be more focused on fixing the "weakening algorithm". Doing a new lesson and achieving that lesson is usually a peace of cake. But mastering this lesson is not. By doing a new lesson, everybody will finish this probably within 10 minutes. That does not mean, we master this. Redoing this lesson at least 4 times, and doing this lesson within 20 "questions-answers" instead of 35 is a good indication of mastering that lesson.