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Is it possible to pass the locale/language while creating a checkout session?
You can pass the locale parameter with the value of the language you would want the checkout to show in. For example for German, you can pass the value for this parameter as 'de' and 'en' for the English website in the HTML code of the website.
Here's our help doc explaining the advanced configuration for this -https://www.chargebee.com/checkout-portal-docs/drop-in-tutorial.html#advanced-configurations