.env

GOOGLE_API_KEY=...

from dotenv import load_dotenv
from langchain_google_genai import ChatGoogleGenerativeAI

load_dotenv()
llm = ChatGoogleGenerativeAI(
    model="gemini-2.0-flash",
    transport="rest"
)

messages = [
    (
        "system",
        "You are a helpful assistant that translates English to German. Translate the use sentence."
    ),
    (
        "human",
        "I like programming."
    ),
]

ai_msg = llm.invoke(messages)
print(ai_msg.content)

Prompt template

from dotenv import load_dotenv
from langchain_google_genai import ChatGoogleGenerativeAI
from langchain_core.prompts import ChatPromptTemplate

load_dotenv()
llm = ChatGoogleGenerativeAI(
    model="gemini-2.0-flash",
    transport="rest"
)

prompt = ChatPromptTemplate.from_messages(
    [
        (
            "system",
            "You are a helpful assistant that translates {input_language} to {output_language}."
        ),
        (
            "human",
            "{input}"
        ),
    ]
)

chain = prompt | llm

ai_msg = chain.invoke(
    {
        "input_language": "English",
        "output_language": "German",
        "input": "I like programming."
    }
)

print(ai_msg.content)