Are there any ways to change the language on Checkout API?

[ryounosuke]

I found this topic.

Login to Sandbox test account with email and password

I am developing an application that will require vendors to authorize their square accounts to accept payments. I want to enable some people to test the product without actually providing their real Square account info, so I want to give them a Sandbox test account they can use. I need to be able to Add Sandbox test accounts from the Developer dashboard. And then send people email and password credentials that they can use to login to these accounts. Where can I get the email and passwords for…

I thought my problem came with English Sandbox test account, but we were not supposed to be changed the language setting from developer account?

If so, which language settings Checkout API referred to under the sandbox?