Enhancements are as follows:
Character handling is now based on version 4.0 of the Unicode standard. This affects the Character and String classes in the java.lang package, the collation and bidirectional text analysis functionality in the java.text package, character classes in the java.util.regex package, and many other parts of the J2SE. As part of this upgrade, support for supplementary characters has been specified by the JSR 204 expert group and implemented throughout the J2SE. See the article Supplementary Characters in the Java Platform, the Java Specification Request 204, and the Character class documentation for more information.
The DecimalFormat class has been enhanced to format and parse BigDecimal and BigInteger values without loss of precision. Formatting of such values is enhanced automatically; parsing into BigDecimal needs to be enabled using the setParseBigDecimal method.
Vietnamese is now supported in all locale sensitive functionality in the java.util and java.text packages. See the Supported Locales document for complete information on supported locales and writing systems.
Refer also to the documentation at http://java.sun.com/j2se/1.5.0/docs/guide/intl/index.html.