UMSBT

Unknown file format, similar to or containing MSBT files. There is no identifiable magic number.

Use Speculation
According to a 3DLand MSBT Editor, UMSBT files have to be unpacked into MSBT files. Further testing on more UMSBT files (like those in Animal Crossing: New Leaf ) needs to be done to make sure that's correct for all UMSBT files.

Unpacking the UMSBT file then opening it seems to break the files, with lots of  tags added. It's possible that Animal Crossing's UMSBT files contain more data, such as when an appropriate script should be read.