If you look more carefully in your DMG, you have three words inside that are spellt in British English.
1° Spectre rather than Specter. (Page 135 and maybe others.)
2° Cheque rather than Check. (Dragon subscription thingie after page 256.)
3° Search for it yourself, I don't remember which it was. I know there was one, though.
About the metric system:
Either you use the metric system and decimal monetary system for gameplay, or you use the medieval measures with the medieval monetary system* for flavour, but not a half-assed bastard between both. Thanks.
* There are fiduciary units (money) and financiary units (comptability), which aren't the same, coins are worth 2, 3, 5, 6, 7, 12, or 20 other coins, prices aren't fixed, and usually you pay in chicken or pigs anyway.