The complication here is that slots in the prompt template is a list of dicts, not a dict itself. To unpack it you need to loop over all the slots and pull out what you need.
Here’s some sample jinja code that looks for a slot named language and uses its value to change the output language of the LLM:
{% set language = 'English' %}
{% for slot in slots %}
{% if slot.name == "language" %}
{% set language = slot.value %}
{% break %}
{% endif %}
{% endfor %}
Your responses should be in {{ language }}