When using CMB2 and WPML it may be useful to style "copy" fields differently, on translated posts edit screen, so the user knows it makes no sense to edit them.

style_cmb2_copy_fields_as_readonly.php

<?php

add_action( 'admin_head', 'style_cmb2_copy_fields_as_readonly', 9999 );

function style_cmb2_copy_fields_as_readonly() {
	$screen = get_current_screen();
	//var_dump($screen);
	if ( $screen->base == 'post' ) {
		global $post, $sitepress;
		if ( isset($post) && isset($sitepress) ) {
			//Original post or translation?
			$original_post = false;
			if ( $trid = $sitepress->get_element_trid( $post->ID, 'post_'.$post->post_type ) ) {
				if ( $translations = $sitepress->get_element_translations( $trid, 'post_'.$post->post_type ) ) {
					foreach( $translations as $translation ) {
						if ( $translation->element_id == $post->ID && is_null($translation->source_language_code) ) {
							//Original post
							$original_post = true;
							break;
						}
					}
					//Not the original post? Go ahead
					if ( !$original_post ) {
						$readonly_fields = array();
						$translation_management = $sitepress->get_setting( 'translation-management', array() );
						foreach( $translation_management['custom_fields_translation'] as $key => $value ) {
							if ( intval($value) == 1 && substr($key,0,1) != '_' ) {
								$readonly_fields[] = $key;
							}
						}
						if ( count($readonly_fields)>0 ) {
							?>
							<style type="text/css">
							<?php
							foreach($readonly_fields as $field) {
								?>
								.cmb2-id-<?php echo str_replace( '_', '-', sanitize_html_class( $field ) ); ?> {
									opacity: 0.25;
								}
								<?php
							}
							?>
							</style>
							<?php
						}
					}
				}
			}
		}
	}
}