This is about saying goodbye in a different language than the movie's dubbing. In Spain (i'm spanish -not 'spaniard'- ) that's the whole point. If Constantino Romero , the actor who dubbed Arnie, had said that in Spanish, the effect wouldn't have been the same.
On the other hand, 'Cheerio then' is the Japanese way to pronounce english words. They add random suffixes to adapt their listening to their pronunciation.
That it's all about.
¡Hasta luego, Lucas!