diff --git a/Build/AtlasBuildScripts/build_project_externals.sh b/Build/AtlasBuildScripts/build_project_externals.sh
index b6547aecc6cd94e5df70265b87821a352c5be5eb..4e751592720d6eb60720afed18b95f84993d3f40 100644
--- a/Build/AtlasBuildScripts/build_project_externals.sh
+++ b/Build/AtlasBuildScripts/build_project_externals.sh
@@ -1,4 +1,4 @@
-# Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
+# Copyright (C) 2002-2023 CERN for the benefit of the ATLAS collaboration
 #
 # Script that is used by the build_externals.sh scripts of the individual
 # projects.
@@ -147,6 +147,14 @@ source "${ATLAS_BUILD_SCRIPTS_DIR}/TDAQ_RELEASE_BASE.sh"
 # Include the timing function.
 source "${ATLAS_BUILD_SCRIPTS_DIR}/atlas_build_time.sh"
 
+# Set the shell's language, in case it's not set explicitly already.
+if [[ -z "${LANG}" || "${LANG}" == "C" ]]; then
+   export LANG=en_US.UTF-8
+fi
+if [[ -z "${LC_ALL}" || "${LC_ALL}" == "C" ]]; then
+   export LC_ALL=en_US.UTF-8
+fi
+
 # Flag for triggering the build of RPMs for the externals.
 RPMOPTIONS="-r ${ATLAS_BUILD_DIR}"
 if [ "$ATLAS_CI_BUILD" = "1" ]; then