�� is two sets of �

[int[]][char[]]'�'
239
191
189

'{0:x} {1:x} {2:x}' -f 239,191,189
ef bf bd

[int[]][char[]]'�' | %{'{0:x}' -f $_}

efbfbd is UTF8 hex for the replacement character which is shown in ISO-8859-1 as the the chars �

(UTF-16 the hex would be 0xfffd)

and in web broswers would be displayed as �

But how are these characters getting in?

The source files are all UTF-8 now as of #214

$ file _output/arduino/1.6.9/tools/chocolateyUninstall.ps1
_output/arduino/1.6.9/tools/chocolateyUninstall.ps1: UTF-8 Unicode (with BOM) text

$ file _output/arduino/1.6.9/tools/chocolateyUninstall.ps1
_output/arduino/1.6.9/tools/chocolateyUninstall.ps1: ASCII text

But the built files are not? ... wth

^^^ was not specifying UTF8 with WriteAllText