elastic/elasticsearch · error · IllegalArgumentException

language [{}] not support for lower case

Error message

language [{}] not support for lower case

What it means

Error "language [{}] not support for lower case" thrown in elastic/elasticsearch.

Source

Thrown at modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/LowerCaseTokenFilterFactory.java:52

    private final String lang;

    LowerCaseTokenFilterFactory(IndexSettings indexSettings, Environment environment, String name, Settings settings) {
        super(name);
        this.lang = settings.get("language", null);
    }

    @Override
    public TokenStream create(TokenStream tokenStream) {
        if (lang == null) {
            return new LowerCaseFilter(tokenStream);
        } else if (lang.equalsIgnoreCase("greek")) {
            return new GreekLowerCaseFilter(tokenStream);
        } else if (lang.equalsIgnoreCase("irish")) {
            return new IrishLowerCaseFilter(tokenStream);
        } else if (lang.equalsIgnoreCase("turkish")) {
            return new TurkishLowerCaseFilter(tokenStream);
        } else {
            throw new IllegalArgumentException("language [" + lang + "] not support for lower case");
        }
    }

}

View on GitHub (pinned to db6a809a66)

When it happens

Trigger: Thrown at modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/LowerCaseTokenFilterFactory.java:52 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of elastic/elasticsearch@db6a809a66 (2026-08-12). Data as JSON: /api/errors/dada1eff1148c4cc. Report an issue: GitHub.