extending Dockerfile with lang and locale settings

changing debian mirror for faster installation

Dockerfile

@@ -7,6 +7,21 @@ ENV PYTHONDONTWRITEBYTECODE=1
 ENV FLASK_ENV=production
 ENV FLASK_SECRET=production-secret-change-me
 
+# Set apt sources to use a faster mirror: https://mirror.init7.net/debian/
+RUN sed -i 's|http://deb.debian.org/debian|https://mirror.init7.net/debian|g' /etc/apt/sources.list
+
+# Update lang and locale settings
+ENV LANG=en_US.UTF-8
+ENV LC_ALL=en_US.UTF-8
+RUN apt-get update && apt-get install -y locales
+RUN sed -i 's/# en_US.UTF-8 UTF-8/en_US.UTF-8 UTF-8/' /etc/locale.gen && locale-gen en_US.UTF-8
+RUN update-locale LANG=en_US.UTF-8
+ENV LANG en_US.UTF-8
+ENV LANGUAGE en_US:en
+ENV LC_ALL en_US.UTF-8
+ENV TZ=Etc/UTC
+RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
+
 # Install system dependencies
 RUN apt-get update && apt-get install -y \
     gcc \