cf_translate_get_current_language-1.php

<?php
/**
 * Always "es" language for Caldera Forms Translation when a locale is called for, such as "es_US"
 */
add_action( 'cf_translate_get_current_language', function( $language ){
	if( 0 === strpos( $language, 'es' ) ){
		$language = 'es';
	}
	return $language;
}, 15 );

/**
 * Always 2 letter codes for lanague -- all languages
 */
add_action( 'cf_translate_get_current_language', function( $language ){
	if( 2 < strlen( $language ) ){
		$language = substr( $language, 0, 2 );
	}
	return $language;
}, 15 );

cf_translate_get_current_language-2.php

<?php
/**
 * Change Caldera Forms Translation language based on alternative GET var
 */
add_action( 'cf_translate_get_current_language', function( $language ){
	if( isset( $_GET[ 'language' ] ){
		$language = strip_tags( $_GET[ 'language' ] );
	}
	return $language;
}, 15 );