Boringly, there aren't many Terry Pratchett books available in Welsh and only one Discworld, as yet. Leaving aside the issue that for many Welsh people, English
is the foreign language, we have...
Llyfrau sydd wedi eu cyfieithu i'r Gymraeg:-
Joni a'r Meirwon (ISBN 086074132X)-- Cyfieithiad Aled P. Jones o Johnny and the Dead
Dim Ond Ti All Achub y Ddynoliaeth (ISBN 0860741443)-- Cyfieithiad Aled P. Jones o Only You Can Save Mankind
Lleidr Amser (ISBN 1904357008)-- Cyfieithiad Dyfrig Parri o Thief of Time
It looks as if the Johnny Maxwell books have made it, but Discworld is yet to make a cultural impression.
(Dyfrig Parri is named as Pratchett's Welsh translator, at least of Thief of Time
Used to be too clever by half, but by virtue of consistent drinking, now only too clever by about a quarter. Banned from all BBC messageboards for being too much of an "uncceptable editorial risk".