You may want to use the native2ascii utility provided by JDK to convert non-ascii characters into escaped unicode values. This utility is available at <jdk-install-dir>/bin
To use the native2ascii utility, enter non-ascii characters for the corresponding values in the properties file and save it.
Use the command, native2ascii -encloding <native_encoding> <src_filename> <target_filename>
native_encoding represents the encoding used to create the source file, src_filename represents the source file and target_filename represents the i18n.properties file.