[taneliv]

Can pgsql fts do stemming or more complex lemmatisation for languages other than English? Or ranking of results based on Okapi BM25 or similar? I was looking into this about two years ago and those were the features in favor of Lucene (basis of ES and Solr).

[kuschku]

Pgsql can do stemming and everything it can do in English also in several dozen languages, including German, French, Spanish, and any for which you install dictionaries. It’s quite useful

[rpedela]

As far as I am aware, it does not support BM25. See pilif's comment about multiple language support.