Install locales used by our tests in before_install.sh

Previously this was done in the GitHub CI script, but this isn't
specific to GitHub, so do it in the common script to make these locales
also available under Cirrus CI.

Also switch to just installing locales-all instead of installing locales
and then running locale-gen because this is simpler and actually works
(locale-gen would have only worked if we modified /etc/locale.gen before
running it, but we didn't).

.github/workflows/ci.yml

@@ -148,13 +148,12 @@ jobs:
 
               # Explanation for installing some less obvious packages:
               #   - coreutils contains nproc used in proc_count.sh called below.
-              #   - locales contains locale-gen also used below.
               #   - Python can't be installed using the action as usual because
               #     it installs an ABI-incompatible version, see (wrongly, IMO)
               #     closed https://github.com/actions/setup-python/issues/370
               #   - xvfb is used for running the GUI tests.
               apt-get update -qq
-              apt-get install -qq coreutils ${compiler-g++} git locales make pkg-config python3 python3-pip sudo xvfb
+              apt-get install -qq coreutils ${compiler-g++} git make pkg-config python3 python3-pip sudo xvfb
               ;;
 
             '')
@@ -223,10 +222,6 @@ jobs:
 
           echo "wxMAKEFILE_CXXFLAGS=$wxMAKEFILE_CXXFLAGS $error_opts" >> $GITHUB_ENV
 
-          # Install locales used by our tests to run all the tests instead of
-          # skipping them.
-          sudo locale-gen de_DE.utf8 de_CH.utf8 en_US.utf8 fr_FR.utf8 sv_SE.utf8
-
           ./build/tools/before_install.sh
 
       - name: Show build environment