这有帮助，但不是完全有帮助。
https://tex.stackexchange.com/questions/69901/how-to-typeset-greek-letters
Package greek-fontenc Error: character �\GenericError {(inputenc) }{Package inputenc Error: Invalid UTF-8 byte "91}
平均能量损失
\usepackage[T1,T2A,LGR]{fontenc}
\usepackage[utf8]{inputenc}\usepackage[polutonikogreek,latin,english,german,french,dutch,italian,spanish,russian]{babel}
\begin{document}
\begin{otherlanguage}{polutonikogreek}(Εὐχολόγιον τὸ μέγα σὺν ϑεῷ ἁγίῳ)\end{otherlanguage} 1873 – большой, и \begin{otherlanguage}{latin}Liturgia Graeca\end{otherlanguage} \begin{otherlanguage}{polutonikogreek}(Μικρὸν εΰχολόγιον σὺν ϑεῷ ἁγίῳ)\end{otherlanguage} 1872 - малый. Который для Вас предпочтительнее?
\end{document}
答案1
您使用的是ϑ（U+0391 希腊符号 THETA）而不是θ（U+03B8 希腊小写字母 THETA）。
添加符号的等价物（或使用字母）。使用 U+0391 不会得到“开放的 theta”；字形取决于字体。
\documentclass{article}
\usepackage[T1,T2A]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[polutonikogreek,latin,english,german,french,dutch,italian,spanish,russian]{babel}
\DeclareUnicodeCharacter{03D1}{\texttheta}
\begin{document}
\begin{otherlanguage}{polutonikogreek}(Εὐχολόγιον τὸ μέγα σὺν ϑεῷ ἁγίῳ)\end{otherlanguage}
1873 – большой, и \begin{otherlanguage}{latin}Liturgia Graeca\end{otherlanguage}
\begin{otherlanguage}{polutonikogreek}(Μικρὸν εΰχολόγιον σὺν ϑεῷ ἁγίῳ)\end{otherlanguage}
1872 - малый. Который для Вас предпочтительнее?
\end{document}
