Using rticles::mdpi_article by @dleutnant (thank you sir), I have an issue with Unicode characters contained in the text (and probably the bibliography as well). I can reproduce the bug on the default mdpi_article Rmd by throwing e.g. Δ somewhere in the text.

! Package inputenc Error: Unicode character Δ (U+0394)
(inputenc)                not set up for use with LaTeX.

xelatex seemed like the solution but mdpi_article doesn't seem to support it. Using:

output: 
  rticles::mdpi_article: 
    latex_engine: xelatex

on the default mdpi_article template gives

! Undefined control sequence.
\set@color ->\pdfcolorstack 
                            \@pdfcolorstack push{\current@color }\aftergroup...
l.1457 \color{black}

So I used a preamble to insert definitions

\DeclareUnicodeCharacter{2009}{\,}
\DeclareUnicodeCharacter{2300}{$\oslash$}
% ... more unicode characters!

With

output: 
  rticles::mdpi_article: 
    includes:
      latex_engine: pdflatex
      in_header: "preamble.tex"

But the list of unicode characters I need to define is increasingly long an it seems like I'll have to define the whole UTF-8 set!

Is there a way to make the mdpi package use xelatex, or support utf8 and resolve the issue once for all, or I should just spend that time declaring utf characters in the preamble?

For context, I'm converting papers originally written in Word and Google docs. I would probably have used the math notation if I was writing the Rmd directly, although I like having the symbols in the RMD (in Rstudio at least), it reads nicely.

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