Convert l10n properties resource bundles to UTF-8 native

L10n properties files are now encoded in ISO-8859-1, thus all the characters outside of that charset are encoded into unicode escapes (`\uXXXX`). From the readability point of view, it is inconvenient and hard to review the contents.
JDK's .properties files are first compiled into ListResourceBundle and then built into .class files. Careful consideration may be needed there.