I used this the other day:
...
(:import (goog.i18n NumberFormat)
(goog.i18n.NumberFormat Format))
...
(def formatter (NumberFormat. Format/COMPACT_LONG))
(.format formatter 4356555555) ;;=> "4.4 billion"
(.format (NumberFormat. Format/COMPACT_SHORT) 4356555555) ;;=> "4.4B"
I believe there are a lot of i18n options for this as well.