When using a sane IDE such as Eclipse, this is already automatically done when you create a .properties file in a Java based project and use Eclipse's own editor. Eclipse will transparently convert the characters beyond ISO-8859-1 range to \uXXXX format. See also below screenshots (note the "Properties" and "Source" tabs on bottom, click for large):
Reference: http://stackoverflow.com/questions/4659929/how-to-use-utf-8-in-resource-properties-with-resourcebundle
Unicodes:
http://unicode-table.com/en/
