The UK and the US both speak english. Wikipedia is in english.
Actually Wikipedia is not only in English.
The 20 largest Wikipedias (February 10, 2005):
English (471035)
German (Deutsch) (197941)
Japanese (99658)
French (Français) (81095)
Swedish (Svenska) (60460)
Polish (Polska) (55451)
Dutch (Nederlands) (51616)
Spanish (Español) (41468)
Italian (Italiano) (34337)
Portuguese (Português) (30946)
Danish (Dansk) (22305)
Esperanto (20594)
Chinese (20197)
Norwegian (17479)
Finnish (Suomi) (14983)
Hebrew
Ukrainian (14151)
Bulgarian (13302)
Catalan (Català) (12193)
Romanian (Românã) (11193)