Also known as: Astérix y la sorpresa del César
"Obelix falls for a new arrival in his home village in Gaul, but is heartbroken when her true love arrives to visit her. However, the lovers are kidnapped by Romans; Asterix and Obelix set out to rescue them on a dangerous journey that will involve gladiators, slavers and beauracracy - and a personal encounter with the Emperor himself, Julius Caesar..."
(Above taken from here).
I looked for an English trailer, but couldn't find one. however, if you click here for an amusing little trailer for the series in general (yes, it is in English). The scenes may be from this actual movie, but I'm not sure. I'm going with it though, because it's the only English one that seemed to come up - that would play for me so I could be sure it was in English - when I searched.
Anyway, it was an enjoyable movie! :)