The "Thailand" tag already exists but it does not belong to any community yet and it is quite famous, so the best is to use it and make something of it. As you are starting you must create a graphic identity for your community, logo banner etc... after you have to reach out to some people that use this tag in the past and make them subscribe and post in the community, I often post about Thailand in English. You have to write in the description that the community is talking about Thailand in English