Changing the encoding of the script to UTF-8 with BOM solved the issue.
I was using SublimeText with the EncodingHelper plugin to control the character-set of the script. It was set correctly to UTF8.
I changed the encoding of the script in SublimeText to “UTF-8 with BOM” and the output was shown correctly.
I created the same script with Notepad++, which defaults to “UTF-8 with BOM”, and the string was shown correctly in the console.
I changed the encoding of the script in Notepad++ to “UTF-8 without BOM” and it was shown incorrectly.
It seems PowerShell cannot guess correctly the encoding of UTF-8 files with no BOM.