O henry stories..

there are phrases I do not understand at all in O.Henry's stories
well maybe because English is not my first language
Yet I have read many English works and I am confident
that I have read more English books than ones in my native language..
therefore I have very little problem reading English literature works
but boy O henry's works leaves me desperately puzzled
there are several phrases and expressions I do not understand at all
I wonder if it is same for all you guys..
and if it is why is it so?? Do you guys also have problems with
many phrases in O. Henry's works?

O'Henry uses the weird language of the common people and I believe it is also a great difficulty for the natives to understand his works perfectly enough.

You wrote that as a non-native speaker you have trouble understanding O. Henry. That's because he used a lot of slang of the time that now gives even native speakers a hard time. The best example comes from his book "Cabbages and Kings," which takes place in Central America. The protaganist receives a telegram written in American slang so that no one but a native speaker could understand it:
"His Nibs skedaddled yesterday per jack-rabbit line with all
the coin in the kitty and the bundle of muslin he's spoony
about. The boodle is six figures short. Our crowd in good
shape, but we need the spondulicks. You collar it. The main
guy and the dry goods are headed for the briny. You know
what to do."

His Nibs = the ruler of the country
skedaddled = ran away quickly
jack-rabbit line = a trail through the countryside
all the coin in the kitty = all the money in the treasury
the bundle of muslin = young, attractive girl
spoony about = in love with
boodle = money
six figures short = missing 100,000
Our crowd = our group
spondulicks = money
You collar it = you get it
main guy = the ruler
dry goods = the girl
briny = ocean

Thanks - English is my first language but I didn't know the meaning of "bundle of muslin" or "spondulicks!

Read the story but am unable to understand how it ends..what is the track of the Duchess got to do with story..Why was Marie murdered..?