System is configured to use Suzhou numerals as custom standard digits.

QLocale::system().toString(50) generates the following codepoints

U+300C U+3007

The correct sequency would be

U+3025 U+3007

(see also https://en.wikipedia.org/wiki/Suzhou_numerals)

The problem seems to be, that the digits for 0-9 are not consecutive starting at U+3007.

Instead 1-9 are located starting at U+3021.