Google Translate API Pricing

This is a Google Cloud Translating API page
Cloud Translation API document

I would like to Transtaion API for slack.

function that to make
– when user write Japanese in slack, slack bot change sentence into English.

Official document
0-1 billion characters(1,000,000,000)
Translation $20 per 1,000,000 characters
Language Detection $20 per 1,000,000 characters

What is language detection?
-> Determine what language is.

What should I do?
-> Check PHP sample for google translation API.

Here is GHE repository and get code.

Translation API is convenient, but it feel like somewhat expensive.