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A general description is here.
Non-ASCII characters were only working correctly in Hershey fonts if these were specified by the 'vfont' argument to text() and not if specified as a font family.
There were several errors in Hershey$allowed, but the help page listed the allowed combinations correctly.
text() no longer attempts to use 'vfont' with an expression for 'labels' (it was documented not to work).