Don't default to US-specific locale settings (#2096)

images/docker-stacks-foundation/Dockerfile

@@ -38,6 +38,7 @@ RUN apt-get update --yes && \
     wget && \
     apt-get clean && rm -rf /var/lib/apt/lists/* && \
     echo "en_US.UTF-8 UTF-8" > /etc/locale.gen && \
+    echo "C.UTF-8 UTF-8" >> /etc/locale.gen && \
     locale-gen
 
 # Configure environment
@@ -46,9 +47,9 @@ ENV CONDA_DIR=/opt/conda \
     NB_USER="${NB_USER}" \
     NB_UID=${NB_UID} \
     NB_GID=${NB_GID} \
-    LC_ALL=en_US.UTF-8 \
-    LANG=en_US.UTF-8 \
-    LANGUAGE=en_US.UTF-8
+    LC_ALL=C.UTF-8 \
+    LANG=C.UTF-8 \
+    LANGUAGE=C.UTF-8
 ENV PATH="${CONDA_DIR}/bin:${PATH}" \
     HOME="/home/${NB_USER}"