The referenced terminal message no longer appears. The upstream
polyglossia issue has been fixed:
https://github.com/reutenauer/polyglossia/issues/337
# Beamer fails also with XeTeX
export/examples/ar/Presentations/Beamer_.*_systemF
-# terminal message: "Language hebrew not found in language.dat.lua"
-export/.*/he/.*(dvi3|pdf5)_systemF
-export/export/latex/languages/supported-languages_(dvi3|pdf5)_systemF
-
# Fails with TL19 but solved in TL20
# Babel with non-TeX fonts fails for some supported languages