(Hmm... street teamer ahoy?)
Their website does have an English version. The tour dates are listed only in Japanese (at
http://www.larc-en-ciel.com/jp/popup/Tour2007.html ), but they're all for Japanese cities.
There's no real market in the U.S. for commercial Japanese music. To have much of a following here, Japanese projects generally need to have some sort of indie/underground cred and/or critical acclaim (Pizzicato Five, Fantastic Plastic Machine, the Boredoms, Ryuichi Sakamoto, etc.). I think Puffy (a.k.a. Puffy AmiYumi) sort of squeezed in because of their retro-pop sound, and they were spun as "offbeat."
I can't remember what the L'Arc-En-Ciel vocalist's English diction is like, but that also poses a stumbling block for a lot of Japanese artists. Pizzicato Five's Maki Nomiya has very good English diction, but Aco and a lot of others don't. Fantastic Plastic Machine used a Japanese vocalist in an English-language song on his album "Beautiful," and I remember wincing when I heard her sing, "Set me free and fry away."