ci: generate multibyte locales for the GNU testsuite

.github/workflows/GnuTests.yml

@@ -49,6 +49,19 @@ jobs:
 
     # Omit installing part of https://github.com/actions/runner-images/tree/main/images/ubuntu
 
+    ### Locales
+    # Several testsuite scripts guard themselves with require_*_locale_ and
+    # silently skip when the locale is missing, which hides both regressions
+    # and improvements in the multibyte code paths.
+    - name: Generate the locales required by the testsuite
+      shell: bash
+      run: |
+        ## Generate the locales required by the testsuite
+        sudo localedef -i en_US -f UTF-8 en_US.UTF-8
+        sudo localedef -i ru_RU -f UTF-8 ru_RU.UTF-8
+        sudo localedef -i el_GR -f ISO-8859-7 el_GR.iso88597
+        locale -a
+
     ### Build
     - name: Build Rust sed binary
       shell: bash

util/run-gnu-testsuite.sh

@@ -56,6 +56,11 @@ usage() {
     echo "Setup:"
     echo "  To get the GNU sed testsuite for comprehensive testing:"
     echo "    git clone https://github.com/mirror/sed.git ../gnu.sed"
+    echo ""
+    echo "  Multibyte tests are skipped unless these locales are installed:"
+    echo "    sudo localedef -i en_US -f UTF-8 en_US.UTF-8"
+    echo "    sudo localedef -i ru_RU -f UTF-8 ru_RU.UTF-8"
+    echo "    sudo localedef -i el_GR -f ISO-8859-7 el_GR.iso88597"
 }
 
 log_info() {
@@ -352,6 +357,10 @@ require_ru_utf8_locale_() {
 }
 
 require_el_iso88597_locale_() {
+    # Check if el_GR.iso88597 locale is available (glibc may spell it iso-88597)
+    if locale -a 2>/dev/null | grep -qi 'el_GR\.iso-\?88597'; then
+        return 0
+    fi
     skip_ "el_GR.iso88597 locale not available"
 }