I've accidentally have found that using Spanish language with `babel` package causes compilation error:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[spanish]{babel}

\begin{document}

Holla, Mundo
\end{document}

the error is:

! Undefined control sequence.
l.105 \ifes@LaTeXe

it seems that this macro is no longer used in babel. When searching for this error I've even found some blog posts about this error with a quick fix:

\let\ifes@LaTeXe\iftrue

unfortunately, no one posted a bug report, so we couldn't fix that in the sources.

Attached patch uses original test which was used in babel for deciding whether LaTeX or other format is used.