There is an issue with lualatex which comes about when using a document such as this (based on a discussion here https://tex.stackexchange.com/questions/525898/combining-french-and-greek-babel-does-not-work-in-dvilualatex/526020?noredirect=1#comment1331448_526020).

Try running lualatex on the following document, and an error will be returned. This seems to apply for all fonts whose packages were generated by autoinst (step is just an example).

\documentclass[12pt]{article}

\usepackage[utf8]{luainputenc}\usepackage[LGR,T1]{fontenc}\input{lgrenc.dfu}

\usepackage{step} \usepackage[greek.ancient,main=french]{babel}

\title{Ça marche?} %\date{} \author{me}

\begin{document} \maketitle un, deux, trois \foreignlanguage{greek}{ἀγαγεῖν} \end{document}

According to Marcel Krüger, this is related to an issue which was reported over a year ago: https://mailman.ntg.nl/pipermail/dev-luatex/2018-November/006138.html.