Check if LANG is set in configure.sh

Tried configuring dbmarlin on a RHEL7.9 box. It took some time to figure out why it did not succeed, but configure passes $LANG down to postgres lc_messages. When LANG is not set, havoc awaits;-). A simple test in configure would avoid that:

<pre>
if (( $EUID == 0 )); then
"Please don't run as root. We recommend you create a dbmarlin user."
exit
fi

• LANG=$(locale | grep "LANG")
• if [ -n ${LANG} ]; then
• echo "Please set LANG, i.e. export LANG=<your choise>";
• exit 1;
• fi

DIR="$(cd "$(dirname "$0")" && pwd)"
</pre>