"This one is the good mountain's front side."
Translation:Kesy sȳro blēno naejon issa.
Since kesy refers to naejon and naejon is inanimate, shouldn't it be kesor ?
No. "Kesy", in this case, is separate from "naejon", which is why it's translated as "This (one)". It's the same in similar "this is X" constructions. It would be "keson naejon", though, if it was "this front".
I actually meant to say "kesir", the inanimate version of kesy, which also stands on its own.
Kesir and kesy are both inanimate, but kesir is for uncountable and abstract things, while kesy is for countable and concrete things.