Translation:We are not taking care of the last tree.
I think that's a second meaning of the sentence, but perhaps more common ways to say it would be:
Poslední strom nás nezajímá. O poslední strom se nezajímáme. Na posledním stromu nám nezáleží.
I'm not a native speaker though, so confirmation from one would be appreciated.
I think the TTS voice is reading it as the letter "O," not the Czech word "o." For example, in the Polish course the TTS voice reads the Polish word "w" as "vu" and the Polish word "z" as "zet.'
o+posledni strom = object my=subject se nestarame=predicate so: My se nestarame o posledni strom. Subject is not necessary.
Because strom is an inanimate masculine noun. Nestaráme se o koho/co. Strom is a co, not a koho.
You "take care of" something, but you "care for" something. You never "take care for" anything. It's incorrect
Good question for a Czech. In English, caring about something is different than caring for something or taking care of something
"We are not looking after that last tree" was deemed incorrect by DL? "Taking care of" and "looking after" mean the same thing in English