Scala String interpolation with Format, how to change locale?

Using the same Java library number formatting support accessible from StringOps enriched String class, you could specify another locale just for that output:

"%.2f".formatLocal(java.util.Locale.US, a)

(as described in "How to convert an Int to a String of a given length with leading zeros to align?")

The Scala way would be to use the string f interpolator (Scala 2.10+), as in the OP's question, but it is using the "current locale", without offering an easy way to set that locale to a different one just for one call.

Locale.setDefault(Locale.US)
println(f"$a%.2f")