I'd just point out that "I have finished THE school successfully" is not a good translation, especially if it's the main translation.
I could imagine it if, say, you were painting the school building and you finished painting it the way it should have been done. But a native speaker, at least in the US, would almost certainly say, "I have finished school successfully."
In this sentence, the translation for the word "skončil" is given as "is over", when you hover the mouse over it. The correct translation for the word in the sentence, however, is "to finish". Shouldnt this also be shown in the translation while hovering? Ive also reported it using the report tool.
Hover translations are generated automatically don't take them for granted! They simply say that in some sentences in the course, it was translated in this way, that's all. It's like looking to the dictionary - you'll always find a bunch of words there but you have to decide whether it's correct to use the specific one in your specific sentence...
Duolingo does have control over the hover hints. Admins can modify them or group them, and such is needed here.