I wouldn’t really support language-specific topics but one common way to do it is to implement community topics. They don’t necessarily have to cater to a specific language, rather, a specific location or community, such as an Australia topic, or a Texas topic or an Indonesia topic. People can discuss their local community events and organize meet-ups and whatnot, or if a person decides to vacation to that location, they can post in that community topic and let the others from that community know so they can potentially meet up.
As such, if one makes an Indonesia topic, it would naturally follow that people can sometimes use Indonesian there aside from the usual English. Of course, it would only be limited to that topic.
Also, community topics would and should only be used for community-related discussion. Any Key-related discussion should be discussed in its appropriate topic, and in English