The only non-japanese shmups on the Dreamcast are the afterparty releases from NGev and Red Spot Games, but none of them are Xeonon 2'ish, although most of them do have the euroshmup feel, which may be what you're looking for?
Jap shooters are usually no problem, almost all of the menu's are in English you just need a way to boot them (chipped, utopia boot disk). I buy a lot of Jap shooters for all systems as you can usually play them easily without knowing any Japanese.
As slk486 said, Sturmwind is a fine release and well worth the cash, albeit it takes a while for them to send it!
There's a few good side scrolling shmups for the DC though: chaos field, gigawing 1&2, mars matrix, psyvariar, and my all time favourite Ikaruga.
I think they are mostly available in PAL but you can use a boot disk to swap region, or if you have a mil cd capable machine you can play pre-patched games.