JDK-8244843 backported additional localisation data for JavaTimeSupplementary, including introducing localisations for the in locale for the first time.
However, in later OpenJDK versions, the locale data is in sun.text.resources.ext, while in 8u, they reside in sun.text.resources.${locale}. The package was not changed in backporting the in JavaTimeSupplementary localedata, so it ends up in sun.text.resources.ext on its own. This also leads to it ending up in rt.jar, rather than being filtered into ext/localedata.jar.
Changing the package fixes both issues. On a patched build,
$ jar tf ~/builder/8u-dev/images/j2sdk-image/jre/lib/ext/localedata.jar |grep _in
sun/text/resources/in/FormatData_in_ID.class
sun/text/resources/in/FormatData_in.class
sun/text/resources/in/JavaTimeSupplementary_in.class
sun/util/resources/in/CalendarData_in_ID.class
sun/util/resources/in/LocaleNames_in.class
sun/util/resources/in/CurrencyNames_in_ID.class