First we'd shoot the aliens. Actually, we'd shoot them no matter what they said. They could be waving peace signs and saying "We come in peace with gifts of knowledge and technology" and we'd still shoot the space hippies.
Then, the Americans and British, seeing the superior aliens use English, would then procede to decalre English the interstellar official language and cease all multilingual government fundings. Then probably nuke France just because. Then probably nuke each other over how "Labour/Labor" is spelled in galatic English.
Actual advanced alien lifeform would be pretty hard for the major western religions to reconcile anyway, even if they didn't make wacky claims about killing dieties.
The Raeliens though, those guys would party like it's 1999. Until we shot them for not doing services in Galatic Standard English, but to be honest, the government's been looking for an excuse to shoot those guys for quite some time.