how to customize/translate BASE_ERROR_CODES

and how to replace or customize the error page of better auth?

Solution

and how to replace or customize the error page of better auth?

You can pass this to your better-auth config to change the error page:

    onAPIError: {
        errorURL: "/my-err-url"
    }

    onAPIError: {
        errorURL: "/my-err-url"
    }

    onAPIError: {
        errorURL: "/my-err-url"
    }

    onAPIError: {
        errorURL: "/my-err-url"
    }

Regarding how to customize/translate error codes, we do give you a way to infer the errors, but it's up to you to translate them: