The example fails for locales where the comma (',') does not happen to be the group separator and the dot ('.') is not the decimal point.
The example is incorrectly assuming en_US locale. It must instead work locale-agnostic. Replace:
to_number ('12,454.8-', '99G999D9S')
with:
to_number ('12,454.8-', '99,999.9S')
I can see the appeal of demonstrating the locale-dependent G and D symbols so that a user becoming familiar with the feature knows that they have options other than just writing out the comma and period literally. If one wants to try the example in a language other than in which the example was written they should modify it so that the literal number being parsed in written in conformance to the locale definition for the language you are using.
