I am creating a multilingual site where one of the languages is Polish. However, when I set it to have a search index built for this language I get a message that it is not supported.
Matt (the project owner of elasticlunr-rs) responded to my message and explained to me that no translation work is necessary (as I wrongly thought) since so-called stop word lists in various languages (including Polish) are already online available. In order to have Polish implemented it is necessary to rewrite a so-called polish stemmer (also available online) in Rust and Javascript. So this is the part that requires some programming. (Implementing non-Indo-Germanic languages is a more involving process, though.)
Matt is busy right now but he might find some time for this in December or January.