You can bring a foreign bike into China as a foreigner but you will need an approved chinese guide by your side all the way. And an approved chinese guide are not cheap as he or she probably need to pay tea money to persons along the way to get to be an approved guide. You will also need an approved itinerary and approved accomodation for absolutely 100 % of your travel. Your guide will arrange this for you. But it will not be cheap - to talk in mild manners.

By the way - I do think Bhutan have quite similar rules and regulations about travelling by a vehicle in their country. You will need an approved guide by your side, approved itinerary, approved accomodation. At least it was like that 4-5 years ago, they might have loosened a bit on their rules since then.

And how are you going to get into Bhutan from China? I am quite sure that Bhutan and China doesnt have any common bordercrossings. Bhutan have only 3 international bordercrossings and those are all to India. Look here for information about travelling to and in Bhutan: http://wikitravel.org/en/Bhutan

And why would you buy a bike in Thailand and try to get vietnam plates on it? I have never heard of anyone doing that and I am afraid that can be a very lenghty process - thats if its possible at ll - something I doubt - that will involve a good bit of time, frustration, and tea money, import duties and additional fees. I cant for my bare black ass understand why you even are thinking about doing it?

By the way - I am not sure vietnam ot thai plated bikes are allowed into China at all - but I could be wrong.

A thai licence is possible to obtain. You will need an adress in Thailand, most likely a permanent adress. Your thai landlord can help you with that. Then copies of passport, visas, health check and vision check papers + additional paperworks that I dont recall for the moment. Then meet at the traffic office for test. Pay some more fees and voila - you might have a thai drivers license.

There are much nicer rice terraces in both Indonesia and The Philippines by the way....

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In the end everything will be fine. If its not fine its not the end....