Here are some tips if you want to seem initiated when you speak to a nyckelharpa player.
Don't call the keys "nycklar" (which means "keys"); people that play call them "knavrar". One "knaver", several "knavrar".
Neither should you call the instrument "nyckelharpa". "Harpa" is what players say. The only time you reallly pronounce the whole word "nyckelharpa" is if there is a risk for a mix-up, making people believe that you talk about one of those harps that angels play, an orchestral harp or some of its folk music relatives .
Execise: "-Vilka schyssta knavrar Du har på harpan!" ("-What cool 'knavrar' your harp has!")