The two are expected to meet again early next month in another Asean meeting in Europe, as well as Hanoi.
Sam Rainsy said the case involves both Cambodia and Vietnam, which makes it international in scope.
Cambodia already has consulates in Seattle, Wash., and Lowell, Mass., in addition to its embassy in Washington.
Protesters were concerned over Cambodia's human rights record and inability to solve longstanding border disputes with its neighbors.
Lemonde joined the tribunal in the office of co-investigating judges in 2006.
Cambodia may still be facing some challenges from the global financial crisis, but it has recently shown some good trends.
Demonstrators plan to protest other issues, including land grabs, evictions, deforestation, and corruption in oil and gas.
A company official said it was following a 2006 decision of the Kandal court that provided 210 hectares to the company.
If Cambodia gives up land, such as the Ta Moan temples of Oddar Meanchey province, he said, “it is going to be endless.”
Kampong Cham province had the most complaints, 18, followed by Takeo with 17, and Phnom Penh, Kandal and Prey Veng with nine each.
The 12 years are added to a two-year sentence Sam Rainsy is already facing for uprooting markers along the Vietnamese border last year.