[Feature]: Support pluggable stemmer for BM25 (enable Polish and other non‑Snowball languages) #654

What feature would you like to request?

Motivation: SnowballStemmer from py_rust_stemmers has no Polish algorithm, so Bm25(language="polish") is impossible even though Polish is a common target language for Qdrant users. Same applies to Czech, Ukrainian, Slovak, Bulgarian, Vietnamese…

Proposal: allow Bm25(stemmer=<callable/obj with .stem_word>, stopwords=[...], language="polish"). Skip supported_languages check when a custom stemmer is provided. Skip stopwords file download when stopwords are provided inline.

Alternative: ship a PolishStemmer wrapping pystempel behind an extra: pip install fastembed[polish].

Is there any additional information you would like to provide?

No response