All default elements, pages and emails served via Paythen are currently available in English only. When creating a plan in Paythen, you can add any text input fields in any language you want. However all default text elements from Paythen will always be shown in English. Any emails sent via Paythen are also in English only.
Payment receipt emails which are sent via your Stripe account will use your Stripe account's language so those can be sent in your local language.
Multi-language support is something we are working on and will be rolling out over time. If you're interested in this, click the chat icon and let us know what languages you want as this helps us better prioritize.