Fix warnings

Dockerfile

@@ -18,7 +18,7 @@ FROM ${BASE_IMAGE}
 ENV DEBIAN_FRONTEND=noninteractive
 
 # Install Webots runtime dependencies
-RUN apt-get update && apt-get install --yes wget xvfb && rm -rf /var/lib/apt/lists/ && \
+RUN apt-get update && apt-get install --yes wget xvfb locales && rm -rf /var/lib/apt/lists/ && \
   wget https://raw.githubusercontent.com/cyberbotics/webots/master/scripts/install/linux_runtime_dependencies.sh && \
   chmod +x linux_runtime_dependencies.sh && ./linux_runtime_dependencies.sh && rm ./linux_runtime_dependencies.sh && rm -rf /var/lib/apt/lists/
 
@@ -32,5 +32,12 @@ ENV PATH /usr/local/webots:${PATH}
 # Enable OpenGL capabilities
 ENV NVIDIA_DRIVER_CAPABILITIES graphics,compute,utility
 
+# Set a user name to fix a warning
+ENV USER root
+
+# Set the locales
+RUN locale-gen en_US.UTF-8
+ENV LANG='en_US.UTF-8' LANGUAGE='en_US:en' LC_ALL='en_US.UTF-8'
+
 # Finally open a bash command to let the user interact
 CMD ["/bin/bash"]