Add unit test for system locale with thousands separator comma
Install en_US.UTF-8 locale in Dockerfile
diff --git a/build/docker/ubuntu-disco/Dockerfile b/build/docker/ubuntu-disco/Dockerfile
index 9775fbb..a175ed5 100644
--- a/build/docker/ubuntu-disco/Dockerfile
+++ b/build/docker/ubuntu-disco/Dockerfile
@@ -255,6 +255,13 @@
# rm swift-4.2.1-RELEASE-ubuntu18.04.tar.gz && \
# swift --version
+# Locale(s) for cpp unit tests
+RUN apt-get install -y --no-install-recommends \
+`# Locale dependencies` \
+ locales && \
+ locale-gen en_US.UTF-8 && \
+ update-locale
+
# cppcheck-1.82 has a nasty cpp parser bug, so we're using something newer
# don't need this on disco, nobody uses it
# RUN apt-get install -y --no-install-recommends \