tinygettext translations with a %s substitution are displaying in English, not the specified language

[jamescdericco]

SuperTux version: SuperTux master commit ab557017188f4d141e8c96d8e031ae89a31c88ae

System information: Fedora Linux 38 (Container Image), kernel 6.6.3-200.fc39.x86_64.

Expected behavior

Running LANG=es ./supertux2 --help should display "Uso: " on the first line of output.

Actual behavior

Running LANG=es ./supertux2 --help actually displays "Usage:", it does not display the Spanish translation as it should.

Steps to reproduce actual behavior

Run LANG=es ./supertux2 --help

Notes

This affects translations throughout SuperTux, not just the command line usage printout. For example, the level intro "contributed by" sentence is also affected by this issue, since its code uses "%s" substitution in the .po files.