Rexx is currently not part of the "Select language..." list.
Migra Software Evolution srl
Rexx is a rather important scripting language in IBM world; it's shared among different platforms, from mainframes to MS-Windows and even Linux. There are many rexx developer teams and many Groups on internet. I really hope BitBucket will shortly manage rexx code with the rigth syntax hilighting. If needed, I could send you (or anybody else) a syntax highlighting sheet for editor like UltraEdit.