If you look at http://min.us/mqWVvDEzp, you'll see that I got an error for "gokai", which is the good answer for translating "Fifth floor", rokkai being the "Sixth floor".

You're right but it depends on American English or English ^^.

Ikkai : first floor (USA)/ ground floor (England)
Nikai : second floor(USA)/ first floor (England)
Sangai: third floor (USA)/ second floor (England)
yonkai : fourth floor (USA)/ third floor (England)
gokai : fifth floor (USA)/fourth floor (England)
So rokkai is "sixth floor" (USA)/ fifth floor (England)
In Japan, floor numbering refers to american way.

Maybe the English version of JA is translated into British English.

Oh ok, quite tricky ^^ Thanks for your answer !

I made the same mistake. Most (if not all) translations here seem to be in American English, so I didn't expect the ground floor to be counted seperately there since I know very well that Americans count floors differently. Maybe the question could be rephrased to make it clearer?

you're right, the English version had a mistake, I actually try to use only American English. I've corrected the question