docker image: install locales and configure en_US.UTF-8 as default

scripts/Dockerfile

@@ -7,7 +7,7 @@
 FROM ubuntu:19.10
 
 # Fix locale to avoid warnings:
-ENV LANG C.UTF-8
+ENV LANG en_US.UTF-8
 
 # Needed for setup:
 COPY ./setup-ubuntu.sh ./setup-android-sdk.sh ./properties.sh /tmp/
@@ -34,4 +34,3 @@ USER builder:builder
 
 # We expect this to be mounted with '-v $PWD:/home/builder/termux-packages':
 WORKDIR /home/builder/termux-packages
-

scripts/setup-ubuntu.sh

@@ -2,6 +2,7 @@
 set -e -u
 
 PACKAGES=""
+PACKAGES+=" locales"
 PACKAGES+=" asciidoc"
 PACKAGES+=" asciidoctor" # Used by weechat for man pages.
 PACKAGES+=" automake"
@@ -79,5 +80,8 @@ curl -O http://security.ubuntu.com/ubuntu/pool/universe/o/openjdk-8/openjdk-8-jr
 sudo dpkg -i openjdk-8-jre-headless_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jre_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jdk_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jdk-headless_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb || sudo apt install -f -y
 rm openjdk-8-jre-headless_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jre_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jdk_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb openjdk-8-jdk-headless_8u212-b03-0ubuntu1."$UBUNTU_VERSION"_amd64.deb
 
+sudo locale-gen --purge en_US.UTF-8
+echo -e 'LANG="en_US.UTF-8"\nLANGUAGE="en_US:en"\n' | sudo tee -a /etc/default/locale
+
 sudo mkdir -p /data/data/com.termux/files/usr
 sudo chown -R $(whoami) /data