Is the r -> ř change predictable? Like how "k" seems to be changed to a "c" when followed by "í"? So "c" and "ř" are these sort of "unofficial" soft versions of "k" and "r" that are actually reflected in the spelling? (Whereas "í" turning "n" soft is not shown in spelling)
Yes, it is.
r -> ř, h -> z, ch -> š, k -> c when followed by -i/-í
You may wish to check the tips & notes for the 'Plurals' skill as well.
On the web, click on the lightbulb when selecting a skill. There are better place to ask these kinds of questions.
Wow! I did not know about that option. Thank you very much for your answer, and for taking the time for letting Duolingo users know about this marvelous tools that enhance the opportunity of having a better experience of learning languages with Duolingo
Start with the Tips and notes or any other grammar resource about the hard adjectival declination (just google Czech adjectives).
I think stare is male, stara is female, and stari is for plural, but I am not completely certain
Jsou oni staři (.,?) Oni jsou staři(.,?) What would be the difference? Is the first applicable for question only? How about the second?