The language [ is not loaded.

[daemonenstall]

Using Texlive 2023 with polyglossia 2.0 my document is compiling just fine, but with Texlive 2024 (polyglossia 2.2) I get the following error:

! Critical Package polyglossia Error: The language [ is not loaded. You must
(polyglossia) load it in order to use it.

And no, I did not try to load a language called "[". In my preambel it looks like this:

\usepackage{polyglossia}
\setmainlanguage{de-DE-1996}
\setotherlanguage{en-US}

The error also occurs when I try to compile an empty document.

[jspitz]

Please give a full minimal example. The following is working for me:

% !TeX TS-program = xelatex
\documentclass{article}

\usepackage{polyglossia}
\setmainlanguage{de-DE-1996}
\setotherlanguage{en-US}

\begin{document}
	Test. \textlang{en-US}{hello}.
\end{document}

[daemonenstall]

Your example is working at my system. The issue is related to reledpar. When I comment it out, the error is gone.
maieul/ledmac#974

% !TeX TS-program = xelatex
\documentclass{article}

\usepackage{polyglossia}
\setmainlanguage{de-DE-1996}
\setotherlanguage{en-US}
\usepackage[series={},nocritical,noend,noeledsec,nofamiliar,noledgroup]{reledmac}
\usepackage{reledpar}

\begin{document}
	Test. \textlang{en-US}{hello}.
\end{document}

[daemonenstall]

Since the reledpar team is already working on the issue, this one can be closed.

[jspitz]

OK, thanks.