I was able to get US hot trends with the following POST request:
"ajax=1&htd=20131111&pn=p1&htv=l"
on the following URL : http://www.google.com/trends/hottrends/hotItems
But how can I get France (or whatever countries) hot trends? I tried hl=fr-FR and even geo=fr, without success.
After searching for a loooong time, I stumbled upon the answer.
Actually, pn=p1 designates the US (the 1 in the p1). One just have to substitute the right code, 16 stands for France:
"ajax=1&htd=20131111&pn=p16&htv=l"
And voilà!
PS: Here are others countries codes:
"ZA":"40"
"DE":"15"
"SA":"36"
"AR":"30"
"AU":"8"
"AT":"44"
"BE":"41"
"BR":"18"
"CA":"13"
"CL":"38"
"CO":"32"
"KR":"23"
"DK":"49"
"EG":"29"
"ES":"26"
"US":"1"
"FI":"50"
"FR":"16"
"GR":"48"
"HK":"10"
"HU":"45"
"IN":"3"
"ID":"19"
"IL":"6"
"IT":"27"
"JP":"4"
"KE":"37"
"MY":"34"
"MX":"21"
"NG":"52"
"NO":"51"
"NL":"17"
"PH":"25"
"PL":"31"
"PT":"47"
"CZ":"43"
"RO":"39"
"GB":"9"
"RU":"14"
"SG":"5"
"SE":"42"
"CH":"46"
"TW":"12"
"TH":"33"
"TR":"24"
"UA":"35"
"VN":"28"