Thank you for your answer, even if I think mIRC should continue to work with non-unicode files for read/write commands.
I converted my previous sample file to utf-8 using Notepad++.
The resulting file is
here The result of $read() is now correct, but I still have a problem with /loadbuf
/loadbuf -tmts @test c:\b.mts
displays * /loadbuf: invalid parameters.