add unicode locale generation to Dockerfile

before the change, unicode characters were displayed in console as question marks

Dockerfile

@@ -15,6 +15,13 @@ RUN touch ${DATA_PATH}/pv-groups.json && \
     ln -sf ${DATA_PATH}/pv-groups.json \
         ${CONFIG_PATH}/plugins/pv-addon-groups/groups.json
 
+# Generate unicode locale so that cyrillic characters display properly
+RUN apt-get update -y && apt-get install -y locales && \
+    echo en_US.UTF-8 UTF-8 > /etc/locale.gen && \
+    dpkg-reconfigure --frontend=noninteractive locales
+ENV LANG en_US.UTF-8
+
+
 VOLUME ${DATA_PATH}