Email from @Kenrick95 (posted with permission):
Two years ago in Wikimania 2015, when I helped you add Indonesian language to Revscoring project, I remembered a moment where we had trouble finding open-licensed Python stemmer for Indonesian language. Few moments ago, I stumbled across this project https://github.com/har07/PySastrawi (which is licensed under MIT license, but the data source is under CC-BY-NC-SA); hope it can be integrated in Revscoring to improve the ORES score of Indonesian Wikipedia. Thanks.
This task is done when the Indonesian stemmer is included in revscoring