Encourage your users to submit translations for your WordPress plugin

plugin.php

<?php
function language_detector_admin_notices() {
	// Get the current language locale
	$language = get_locale();

	// Check if the nag screen has been disabled for this language
	if ( false === get_option( 'plugin_slug_language_detector_' . $language, false ) ) {
		
		// Check if a translation file already exists for this language
		if ( $loaded = load_plugin_textdomain( 'text_domain', false, plugin_dir_path( __FILE__ ) . '/languages/' ) ) {
			// If a translation file is discovered, we disable all future nag screens for this language
			update_option( 'plugin_slug_language_detector_' . $language, true, true );
			return;
		}
		
		// We need the translation data from core to display human readable locale names
		require_once( ABSPATH . 'wp-admin/includes/translation-install.php' );

		$translations = wp_get_available_translations();

		// Gather information about the plugin (in this case we really only watn the name and text domain/slug)
		$plugin = get_plugin_data( __FILE__ );

		printf(
			'<div class="notice notice-info"><p><strong>%s</strong></p><p>%s</p></div>',
			esc_html( $plugin['Name'] ),
			sprintf(
				__( 'This plugin does not have a translation for <strong>%1$s</strong>, you can help translating the plugin at <a href="%2$s" target="_blank">%2$s</a>.' ),
				$translations[ $language ]['native_name'], // The native name of the language currently in use
				esc_url( 'https://translate.wordpress.org/projects/wp-plugins/' . $plugin['TextDomain'] ) // The URL to the translation overview page for our plugin
			)
		);
	}
}

// Hook into admin notices
add_action( 'admin_notices', 'language_detector_admin_notices' );

// Output JavaScript for handling dismissals in the footer
function language_detector_admin_footer() {
	$language = get_locale();

	// We only add our JavaScript if the nag notice is being displayed any way
	if ( false === get_option( '$plugin_slug_language_detector_' . $language, false ) ) {
?>
<script type="text/javascript">
	jQuery(document).ready(function ($) {
		$( ".notice.is-dismissible.language-detect-nag-dismiss" ).on( "click", ".notice-dismiss", function() {
			var data = {
				action : 'language_nag_dismiss'
			};

			$.post(
				ajaxurl,
				data
			);
		});
	});
</script>
<?php
	}
}
add_action( 'admin_footer', 'language_detector_admin_footer' );

// Trigger function for when the ajax call goes through
function language_detector_dismiss() {
	$language = get_locale();

	update_option( '$plugin_slug_language_detector_' . $language, true );
	wp_die();
}
add_action( 'wp_ajax_language_nag_dismiss', 'language_detector_dismiss' );