public Parsable setExplicitLanguage(Optional<Language> language) {
        Objects.requireNonNull(language, "Explicit language cannot be null");
        this.explicitLanguage = language;
        return this;
    }
Returns the language explicitly set to be used when parsing, or empty if none is set.
container-search/src/main/java/com/yahoo/search/query/parser/Parsable.java