Convert markdown to pdf for Cyrillic languages

[mfts]

Problem

Translation into Cyrillic languages cannot be converted to PDF with the current method.

Currently there's an issue on the first Cyrillic letter in the document like this

! LaTeX Error: Unicode character Д (U+0414)
               not set up for use with LaTeX.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.96 \begin

Solution

1. We need to choose a font that supports Cyrillic letters / glyphs
2. Use xelatex as pdf-engine

Proposal

Change the Makefile for Cyrillic languages to

tea.white-paper_%.pdf: i18n/%/white-paper.md i18n/%/metadata.yml tea.csl img/*
	pandoc \
	--number-sections \
	--output $@ \
	--metadata-file i18n/$*/metadata.yml \
	--filter pandoc-crossref \
	--csl=tea.csl \
	--citeproc \
	-V mainfont="Georgia" \    <--- new
	--pdf-engine xelatex \    <--- new
	$<