Tip to anyone using the RunHiddenAdvanced function kindly provided by tbone:
To make it compatible with unicode output, you may need to use the /u switch of cmd.exe and also, for the ReadFile function, adjust the parameters for the OpenTextFile function.
For this case, I also had to make some other changes, as the tool I am using refuses to output unicode to stdout but is able to output unicode by itself with a '--output' switch, so I made RunHiddenAdvanced read that file instead of stdout.