About a month ago, Google announced that 30 more languages would be coming to Google Assistant "over the next few months." The languages mentioned there included Hindi, Indonesian, Norwegian, Swedish, among others. Of those, the only one that has arrived thus far is Hindi, but Indonesian is now taking second place.
Language support is pretty confusing in Google-land. Allo is the only Google voice service that already supported Indonesian, but the newly-added Assistant is the most important one since it's what people will be using from their phones and tablets. Both Pixel phones and non-Pixel devices now support it. Indonesian still isn't available on Google Home and Wear OS, though.
If you're still waiting for your language to be added to Assistant, keep an eye out. We already know that 30 additional ones will be added by the end of 2018, and a leaked presentation revealed that Assistant will become available in 38 more countries by the end of the year as well.
Indonesian is now in the Google Assistant on Android TV, as well.