Adding your own dictionary to the Kobo Touch has been discussed previously (December 2011):
https://www.mobileread.com/forums/sho...d.php?t=159823 That thread also concludes "nope, can't."
I haven't seen a plead for the ability in the Kobo Touch future firmware request thread though (that I can remember anyway). Maybe we should all jump up and down in there asking for either a better dictionary, or the possibility to put your own in:
https://www.mobileread.com/forums/sho...d.php?t=139965 I would also prefer a real UK dictionary for the same reasons Liesse mentions (well, except for the cups and ounces stuff because I get so confused with all that weirdness. Just use ml! Agh!).