It's not until the city overflows with scent of osmanthus, which is also called "fragrant olive", that I realize the coming of autumnautumn has arrived.

There are variety of seasonal tradiassociations such as snow, cherry blossom, fire works, and "the voice" of cicadas in Japan.

"Traditions" is not the right word as those are things that people do. Instead you listed natural features of those seasons, so "associations" means those things are associated with the season. "Features" would work too though.

However, nothing but fragrant olive is all that comes to my mind when I think of which smells tellingcan tell the transition of seasons clearly.

Your sentence is ok, this one feels more natural to me.

Even though roses and plums also give off excellent scents, they aren't enough strong to figure outidentify if you can't see them.

again, "figure out" is ok, "identify" is clearer and more descriptive. Also instead of "give off", "emit" is fun option, "roses and plums emit excellent scents".