Bitnami Developer here,
Weblate is not offered as a LightSail Blueprint. This is the list of apps:

Alternatively, you could launch any of those apps, and install manually the Weblate Stack. For that, you should follow these steps:
- Launch a LightSail instance (e.g. WordPress)
- Access via SSH
- Disable the previous installation:
sudo /opt/bitnami/ctlscript.sh stop
sudo mv /opt/bitnami /opt/bitnami.bak
That way, you will stop all the services and keep a backup of the initial installation. Run the command below if you would like to remove it:
sudo rm -rf /opt/bitnami*
- Install Weblate Stack on your LightSail instance:
wget https://bitnami.com/redirect/to/856398/bitnami-weblate-3.10-0-linux-x64-installer.run
chmod +x bitnami-weblate-3.10-0-linux-x64-installer.run
sudo ./bitnami-weblate-3.10-0-linux-x64-installer.run
I hope it helps