This is one of the original development setups of J2ME. I recommend J2ME Maven instead.
Using Ubuntu 20.04:
sudo dpkg --add-architecture i386
sudo apt update
sudo apt-get install libxi6:i386 libxt6:i386 libxi6:i386 libxtst6:i386 libxext6:i386
./jdk-6u45-linux-i586.bin
sudo mkdir -p /usr/lib/jvm/
sudo mv jdk1.6.0_45/ /usr/lib/jvm/
sudo chown -R root:root /usr/lib/jvm/
./sun_java_wireless_toolkit-2.5.2_01-linuxi486.bin.sh
# set java path to /usr/lib/jvm/jdk1.6.0_45/bin
./WTK2.5.2/bin/ktoolbar