Finally got around to test the methods suggested, and can report as follows:
(a) manually adding [HKLM\ControlPanel\PhoneExtendFunction] to the registry - doesn't work.
(b) changing the 0409.mui with Reshack to use chinese language (1028) - still cannot see text when firing up AdvancedNetwork.exe, whether mui is named 0804.mui or 0404.mui.
(c) found a seeting in [HKLM\MUI] which is defaulting to 1028 (chinese). Change it to 1033, soft reset the machine, and AdvancedNetwork.exe (unmodified) now shows all text - hurray! Used AdvancedNetwork to set authentication to CHAP then back to PAP, then fire up IE - still would NOT connect, with same packet error message!
Looks like the program AdvancedNetworks.exe does not work on the 612c, and have to continue looking for a solution...