Kelsey Grammar had a cold during time of filming hence why his voice sounds slightly raspy in the episode
This episode suggests that Frasier (Kelsey Grammer) and Niles (David Hyde Pierce) do at least understand German. The line Niles quotes is "Ha! Er ist schön, der Knabe!" which translates into "Oh! He is beautiful, this boy!"
In the closing scene Niles (David Hyde Pierce) is in shirt sleeves and suspenders (braces in the UK) in the court room. This is a direct reference to the courtroom scenes in Inherit the Wind (1960), starring Spencer Tracy and Fredric March.
Harlow Safford addresses numerous characters as "Sparky." This may have been a nod to "Peanuts" creator and artist Charles "Sparky" Schulz, who was a fan of "Frasier" and its predecessor, "Cheers."
The line iin German is a Quote from the Caracter Klingsor (the Bad Guy from this Opera ) from Parsifal