我必须使用 XeTeX，因为它有助于在文本和数学模式下设置任意字体（或新数学在数学模式下）。
我注意到该polyglossia软件包的命令有一个错误\normalfont。这里是@egreg 对这个错误的详细描述。
在 MikTeX 中更新软件包（至较新版本）后polyglossia问题得到解决，但是出现了以下错误：
Undefined control sequence. ...ctlanguage *[babelshorthands=true]{russian}
Undefined control sequence. ...ctlanguage *[babelshorthands=true]{russian}
Encoding scheme `' unknown. ...ctlanguage *[babelshorthands=true]{russian}
Undefined control sequence. ^^I\begin{document}
Undefined control sequence. ^^I\begin{document}
Encoding scheme `' unknown. ^^I\begin{document}
Undefined control sequence. ^^I\begin{abstr}
Undefined control sequence. ^^I^^I\par{\normalfont
Undefined control sequence. ^^I^^I\par{\normalfont
Encoding scheme `' unknown. ^^I^^I\par{\normalfont
Undefined control sequence. ^^I\end{abstr}
Undefined control sequence. ^^I\end{abstr}
Encoding scheme `' unknown. ^^I\end{abstr}
Undefined control sequence. ^^I\end{document}
Undefined control sequence. ^^I\end{document}
Encoding scheme `' unknown. ^^I\end{document}
Undefined control sequence. ...ctlanguage *[babelshorthands=true]{russian}
Undefined control sequence. ...ctlanguage *[babelshorthands=true]{russian}
Encoding scheme `' unknown. ...ctlanguage *[babelshorthands=true]{russian}
Overfull \hbox (29.36624pt too wide) in paragraph
在 MWE 中：
\documentclass[extrafontsizes,a4paper,*pt,oneside,openany]{memoir}
\usepackage{fontspec} %[no-math] How can I use the Newton instead of newtxmath?
%\usepackage{newtxmath} %math font of TNR type
\usepackage{polyglossia}[2014/05/21]
\setmainlanguage[babelshorthands=true]{russian} %
\setotherlanguage{english}
\setmainfont{Arial} %%
% \setsansfont{Newton}
% \setmonofont{Newton}
\newenvironment{abstr}{\small\itshape}{\normalfont\normalsize}
\begin{document}
\begin{abstr}
\par{\normalfont Key \textbf{words}.} Hey!
\end{abstr}
\newcommand{\fn}{\expandafter\string\the\font}
{\normalsize\selectfont ха-хаха Book\_name\_ch\_AuthorsSurnames\fn}
\fontname\font\\
$ a+b$
\end{document}
这是一个很好的输出：
如何避免这些错误？请帮帮我！
谨致问候，弗拉基米尔
UPD1MWE 已更新。
UPD2TexStudio 的屏幕截图
更新3：我按照@DavidCarlisle 和@UlrikeFischer 的建议查看了整个日志文件。之后我找到了解决方案这里。