The original Agatha Christie novel "After the Funeral", on which "Murder at the Gallop" is very loosely based, bears the German title "Der Wachsblumenstrauß". I suppose that in the book a bouquet of wax flowers plays some role (at the "funeral"?), but I haven't read it myself.
Unlike the original, the German titles of the movies in the series did not follow a common style, i. e. did not start with something like "Murder...". The first one, "Murder She Said", was called like the book it was based on, "16.50 ab Paddington" (4:50 from Paddington). This is probably why they also named the next film after the corresponding book. Likewise, the novel "Mrs McGinty Is Dead", which became "Murder Most Foul" in the movie series, is called "Vier Frauen und ein Mord" (Four Women and one Murder) in Germany, and so is the movie. (They obviously could not keep this up with "Murder Ahoy!", since this is not based on a Christie book. It became "Mörder ahoi!", meaning "Murderer Ahoy!", by the way.)
I remember (and always found it strange, kind of like a breaking of the "fourth wall") that at least in the German-dubbed version Miss Marple expressly refers to "Agatha Christie's book 'Der Wachsblumenstrauß'" and uses it in finding the murderer. But this is indeed the closest the movie ever gets to having something to do with a bouquet of wax flowers.