From wikipedia it's evident that Manu Smṛtī was followed by Buddhist Kings of aforementioned countries,
The Dharma-sastras, particularly Manusmriti, states Anthony Reid, were "greatly honored in Burma (Myanmar), Siam (Thailand), Cambodia and Java-Bali (Indonesia) as the defining documents of the natural order, which kings were obliged to uphold. They were copied, translated and incorporated into local law code, with strict adherence to the original text in Burma and Siam, and a stronger tendency to adapt to local needs in Java (Indonesia)". The medieval era derived texts and Manusmriti manuscripts in Southeast Asia are, however, quite different than the "vulgate" version that has been in use since its first use in British India. The role of then extant Manusmriti as a historic foundation of law texts for the people of Southeast Asia has been very important, states Hooker.
I wonder to what an extent Manu Smṛtī was followed as in,
- Did they impose class system (Varṇa Vyavashthā)? If yes, was it birth based?
- How did they incorporate Hindu philosophy of Manu Smṛtī onto Buddhist population?
- Can we have specific areas where the Smṛtī was followed? Or it was followed out and out?