Check in the pristine copy of ICU 4.6...

icu46/source/data/icu4j-readme.txt

+********************************************************************************
+* Copyright (C) 2008-2010, International Business Machines Corporation         *
+* and others. All Rights Reserved.                                             *
+*                                                                              *
+* 6/26/08 - Created by Brian Rower - heavy copying from ICU4J readme & others  *
+*                                                                              *
+********************************************************************************
+
+Procedures for building ICU4J data from ICU4C data:
+
+*Setup*
+
+In the following,
+        $icu4c_root is the ICU4C root directory
+        $icu4j_root is the ICU4J root directory
+        $jdk_bin is the JDK bin directory (for the jar tool)
+
+1. Download and build ICU4C. For more instructions on downloading and building
+        ICU4C, see the ICU4C readme at:
+        http://source.icu-project.org/repos/icu/icu/trunk/readme.html#HowToBuild
+        (Windows: build as x86, Release otherwise you will have to set 'CFG' differently below.)
+
+        *NOTE* You should do a full rebuild after any data changes.
+
+
+2. Step 2 depends on whether you are on a Windows or a Unix-type
+platform.
+
+*Windows* 
+
+2a. On the command line, cd to $icu4c_root\source\data.
+
+2b. On the command line,
+        nmake -f makedata.mak ICUMAKE=$icu4c_root\source\data\  CFG=x86\Release JAR="$jdk_bin\jar" ICU4J_ROOT=$icu4j_root  icu4j-data-install
+
+       Continue with step 3 below, in Java:
+
+
+*Linux*
+
+        $icu4c_build is the ICU4C root build directory,
+        which is $icu4c_root/source in an in-source build
+
+2c. On the command line, cd to $icu4c_build
+
+2d. Do
+        make JAR=$jdk_bin/jar ICU4J_ROOT=$icu4j_root icu4j-data-install
+
+       (You can omit the JAR if it's just jar.)
+
+        Continue with step 3, in Java:
+
+*Java*
+
+3. After the ICU4C-side steps above, build the core-data and core-test-data targets of the
+        ICU4J ant build to unpack the jar files  with the following commands:
+
+        cd $icu4j_root
+        ant core-data core-test-data