Board Thread:Support Requests - Getting Started/@comment-28159178-20160409083832/@comment-1117661-20160409091859

Both the language of the wiki and the domain can be changed (incl: to the one without lang prefix if it's foreign enough). You just have to ask through Special:Contact.

Difference when choosing language on creation mostly falls to:
 * Domain prefix (ofc)
 * Language of the interface: like namespaces and what unregistered users see
 * Which starter the contents will be imported from at creation (later change won't import contents second time)

For languages with their own localized starters the best idea is select their language and ask for domain later.

Looking at the current Thai starter you're better off with English one anyway so I recommend creating with English language and then ask for the change ;)