The code in QLocale that serialises numbers uses locale-appropriate digits for base ten.
However, these methods support any base from 2 through 36;
for bases other than ten, they all use, as digits, some initial sub-set of of ASCII 0 through 9 then a through z.
For bases up to ten, it could perfectly sensibly use locale-appropriate digits.
For bases beyond ten, it's not clear what we should do; but switching to ASCII does not seem smart.

On a related note, we should probably check whether there are any duodecimal locales …