The answer to the riddle (not the cipher):
I'm known throughout the world
Even though I'm no more the tallest
For four decades it was the world’s tallest structure but there are lots of taller buildings now
I'm starting to get old
Sad but true.
But one day per year, I'm still on my brightest
My half-sister lives in a far away country
Statue of Liberty was also built by Eiffel (half-sister sharing a father)
Near the ocean, while I'm stuck in the city
is placed pretty near the ocean (on an island).
I could be called an iron lady
That's how the Eiffel Tower is called
But please don't, this one's historically my enemy
Hm.. Some historical facts certainly mention that.
"The answer is the key, in more sense than one?"
As Rubio pointed out:
the numeric strings are geo coordinates:
Eiffel Tower Restaurant in Las Vegas
Eiffel Tower (Paris)
Tokyo Tower - Tokyo, Japan
So the first sense of the answer being a key is
all the locations present some kind of Eiffel Tower.
The second sense is the key to the cipher below as @Ivanhoe commented:
which is Vigenere's cipher with key "EIFFELTOWER"
I am sorry for wrong deciphering - I had some letters mixed up (switched 'p' and 'q' don't ask me why) - now it should be correct (thanks to @Ivanhoe again).
It is from Vegas, so the language is english.
iamtheeighteenthchildofmendeleiev (in english he is spelled Mendeleev, right?)
I am the eighteenth child of Mendeleiev
Argon (Ar) (18th element in Mendeleiev's periodic table)
This is from Paris, so the language is french
Je suis ce quivient avant ce que je possede
I am what comes before what I have.
my, as it comes before i.e. "my car". In french that would be ma, mon or mes.
This is from Tokyo, so the language is japanese
Ichi no ato watashi wa kimasu
I come after one
two which in japanese spells ni
The deciphered parts together make
Armani, Armonni or Armesni
So the password is likely to be: Armani as it is the only proper word from the three (Giorgio Armani is the founder of a famous Italian fashion house).