#!/bin/bash

SED=$(
    while IFS=$'\t' read -r -a myArray
    do
    echo -ne "s_"${myArray[0]}"_"${myArray[1]}"_g;\n"
    done < replacements
)

echo  sed -e "$SED"
cat $1 | sed -e "$SED" | sed -z 's_-\n__g'> $2