Impact of the codec handling changes in Qt6

I am trying to port my project to Qt 6.1. The removal of QTextCodec and related setCodec() functions is really a blocker for me.   I searched here and found QTBUG-86437. However,  the impact of the removal is not limited to file converter applications.

Qt6 assumes all Unix platforms use UTF-8 as local code page. That is not true. Although modern Linux distributions use UTF-8 as default system encoding, we always change User's or Application's default encoding (by setting "LANG" env) to:

  a. meet national standard requirement ("GB18030")

  b. get consistent behavior across Windows/Linux machines 

I know more codec support in QStringConverter is planed for future versions. But something like setCodecForLocale() should be possible for Linux. Otherwise it will be very inconvenient  to port and debug.