Install msgcmp (missing in the docker container)

.gitlab-ci.yml

@@ -58,6 +58,9 @@ translation:
       changes:
         - resources/language/*/strings.po
       when: manual
+  before_script:
+  - *apt_get_update
+  - apt-get install --yes msgcmp > /dev/null
   script:
     - files=$(find . -name strings.po -not -path './resources/language/resource.language.en_gb/*') && for file in files; do msgcmp $file ./resources/language/resource.language.en_gb/strings.po; done