LayerSlider translation into German does not work

here we go – Edit: i think this is the better way to do it :
https://kriesi.at/support/topic/layerslider-translation-into-german-does-not-work/#post-1493597
________________________
(just for standalone plugin – not for the included layerslider)

/**
 * LayerSlider: Auto-Patch for Select Option of lang files
 */

// 1. Daily auto-patch
function child_theme_layerslider_auto_patch() {
    if (!defined('LS_ROOT_PATH')) {
        return;
    }
    
    // Check only once a day
    $last_check = get_option('layerslider_patch_last_check', 0);
    if (time() - $last_check < DAY_IN_SECONDS) {
        return;
    }
    
    child_theme_patch_layerslider_template();
    update_option('layerslider_patch_last_check', time());
}
add_action('admin_init', 'child_theme_layerslider_auto_patch', 999);

// 2. Patch-Function
function child_theme_patch_layerslider_template() {
    $template_file = LS_ROOT_PATH . '/templates/tmpl-plugin-settings.php';
    $locales_dir = LS_ROOT_PATH . '/locales';
    
    if (!file_exists($template_file) || !is_dir($locales_dir)) {
        return false;
    }
    
    // Find available languages
    $available_languages = child_theme_get_available_languages($locales_dir);
    
    if (empty($available_languages)) {
        return false;
    }
    
    $content = file_get_contents($template_file);
    
    // language names
    $language_names = [
        'de_DE' => 'Deutsch',
        'de_DE_formal' => 'Deutsch (Sie)',
        'de_CH' => 'Deutsch (Schweiz)',
        'de_CH_informal' => 'Deutsch (Schweiz, Du)',
        'de_AT' => 'Deutsch (Österreich)',
        // add lang names needed for your uploaded lang files
    ];
    
    // protected default languages 
    $protected_languages = ['auto', 'en_US', 'fr_FR', 'hu_HU', 'uk'];
    
    $modified = false;
    
    // PART 1: Adding missing languages
    $new_options = '';
    foreach ($available_languages as $locale) {
        if (strpos($content, 'value="' . $locale . '"') !== false) {
            continue;
        }
        
        $language_name = isset($language_names[$locale]) ? $language_names[$locale] : $locale;
        $new_options .= "\n\t\t\t\t\t\t<option value=\"" . $locale . "\" <?php echo ( \$custom_locale === '" . $locale . "' ) ? 'selected' : ''?>>" . $language_name . "</option>";
        $modified = true;
    }
    
    if (!empty($new_options)) {
        $search = '<option value="auto" <?php echo ( $custom_locale === \'auto\' ) ? \'selected\' : \'\'?>><?php _e(\'Site default\', \'LayerSlider\') ?></option>';
        $replace = $search . $new_options;
        $content = str_replace($search, $replace, $content);
    }
    
    // PART 2: Removing languages that no longer exist
    foreach ($language_names as $locale => $name) {
        if (in_array($locale, $protected_languages)) {
            continue;
        }
        
        if (strpos($content, 'value="' . $locale . '"') !== false && !in_array($locale, $available_languages)) {
            $pattern = '/\s*<option value="' . preg_quote($locale, '/') . '"[^>]*>.*?<\/option>/';
            $new_content = preg_replace($pattern, '', $content);
            
            if ($new_content !== $content) {
                $content = $new_content;
                $modified = true;
            }
        }
    }
    
    if (!$modified) {
        return true;
    }
    
    // Back up and save
    file_put_contents($template_file . '.backup-' . date('Y-m-d-His'), file_get_contents($template_file));
    file_put_contents($template_file, $content);
    
    return true;
}

// 3. helper function
function child_theme_get_available_languages($locales_dir) {
    $languages = [];
    $files = glob($locales_dir . '/LayerSlider-*.mo');

    if (!$files) {
        return $languages;
    }

    foreach ($files as $file) {
        $filename = basename($file, '.mo');
        $locale = str_replace('LayerSlider-', '', $filename);
        if (!empty($locale)) {
            $languages[] = $locale;
        }
    }   
    return $languages;
}

// 4. Automatically patch after plugin update
function child_theme_layerslider_after_update($upgrader_object, $options) {
    if ($options['action'] !== 'update' || $options['type'] !== 'plugin') {
        return;
    }
    
    if (!isset($options['plugins'])) {
        return;
    }
    
    foreach ($options['plugins'] as $plugin) {
        if (strpos($plugin, 'layerslider') !== false || strpos($plugin, 'LayerSlider') !== false) {
            delete_option('layerslider_patch_last_check');
            child_theme_patch_layerslider_template();
            break;
        }
    }
}
add_action('upgrader_process_complete', 'child_theme_layerslider_after_update', 10, 2);

/**
 * END of LayerSlider: Auto-Patch for Select Option of lang files
 */

Summary of the final solution:
✅ Upload language files to /LayerSlider/assets/locales/
✅ Automatic patch after 24 hours
✅ Automatic patch after plugin updates
✅ when needed: delete_option(‘layerslider_patch_last_check’); – for immediate patch

these snippets will inspect each day – if there are additional lang files for LayerSlider

PS: You can force the patcher by temporarily inserting the following to your child-theme functions.php: delete_option('layerslider_patch_last_check');
after that goto Layerslider Dashboard and : Plugin Updates – Re-Check

this is i think the best option to handle the lang files:
it is a only manual patch vor those lang files of LayerSlider.
Or automatic after Plugin Update
Just uploading the lang-files to /wp-content/plugins/LayerSlider/assets/locales folder

You will have than a button on the LayerSlider Admin bar:

/* ========================================================================
 * LayerSlider: Patch for Select Option of lang files
 * Auto-copies language files from uploads to plugin directory
 * Auto-removes language files that were deleted from uploads
 * Auto-patches after plugin updates
 ======================================================================== */

// 1. Patch-Function
function child_theme_patch_layerslider_template() {

    if (!defined('LS_ROOT_PATH')) {
        return false;
    }

    $template_file = LS_ROOT_PATH . '/templates/tmpl-plugin-settings.php';
    
    // Check both locations
    $plugin_locales_dir = LS_ROOT_PATH . '/locales';
    $upload_dir = wp_upload_dir();
    $custom_locales_dir = $upload_dir['basedir'] . '/layerslider/lang';
    
    if (!file_exists($template_file)) {
        return false;
    }
    
    // Create custom locales directory if it doesn't exist
    if (!is_dir($custom_locales_dir)) {
        wp_mkdir_p($custom_locales_dir);
    }
    
    // SYNC language files (copy new/updated, delete removed)
    child_theme_sync_language_files($custom_locales_dir, $plugin_locales_dir);
    
    // Find available languages (now from plugin directory after sync)
    $available_languages = child_theme_get_available_languages($plugin_locales_dir);
    
    if (empty($available_languages)) {
        return false;
    }
    
    $content = file_get_contents($template_file);
    
    // language names
    $language_names = [
        'de_DE' => 'Deutsch',
        'de_DE_formal' => 'Deutsch (Sie)',
        'de_CH' => 'Deutsch (Schweiz)',
        'de_CH_informal' => 'Deutsch (Schweiz, Du)',
        'de_AT' => 'Deutsch (Österreich)',
        // add lang names needed for your uploaded lang files
    ];
    
    // protected default languages 
    $protected_languages = ['auto', 'en_US', 'fr_FR', 'hu_HU', 'uk'];
    
    $modified = false;
    
    // PART 1: Adding missing languages
    $new_options = '';
    foreach ($available_languages as $locale) {
        if (strpos($content, 'value="' . $locale . '"') !== false) {
            continue;
        }
        
        $language_name = isset($language_names[$locale]) ? $language_names[$locale] : $locale;
        $new_options .= "\n\t\t\t\t\t\t<option value=\"" . $locale . "\" <?php echo ( \$custom_locale === '" . $locale . "' ) ? 'selected' : ''?>>" . $language_name . "</option>";
        $modified = true;
    }
    
    if (!empty($new_options)) {
        $search = '<option value="auto" <?php echo ( $custom_locale === \'auto\' ) ? \'selected\' : \'\'?>><?php _e(\'Site default\', \'LayerSlider\') ?></option>';
        $replace = $search . $new_options;
        $content = str_replace($search, $replace, $content);
    }
    
    // PART 2: Removing languages that no longer exist
    foreach ($language_names as $locale => $name) {
        if (in_array($locale, $protected_languages)) {
            continue;
        }
        
        if (strpos($content, 'value="' . $locale . '"') !== false && !in_array($locale, $available_languages)) {
            $pattern = '/\s*<option value="' . preg_quote($locale, '/') . '"[^>]*>.*?<\/option>/';
            $new_content = preg_replace($pattern, '', $content);
            
            if ($new_content !== $content) {
                $content = $new_content;
                $modified = true;
            }
        }
    }
    
    if (!$modified) {
        return true;
    }
    
    // Save
    file_put_contents($template_file, $content);
    
    return true;
}

// 2. IMPROVED: Sync language files (copy new + delete removed)
function child_theme_sync_language_files($source_dir, $target_dir) {
    
    if (!is_dir($source_dir) || !is_dir($target_dir)) {
        return false;
    }
    
    $copied = 0;
    $deleted = 0;
    
    // PART 1: Copy new/updated files from source to target
    $source_files = glob($source_dir . '/LayerSlider-*.{mo,po}', GLOB_BRACE);
    
    // Get list of locales in source directory
    $source_locales = [];
    if ($source_files) {
        foreach ($source_files as $source_file) {
            $filename = basename($source_file);
            $target_file = $target_dir . '/' . $filename;
            
            // Extract locale from filename
            preg_match('/LayerSlider-([^\.]+)\./', $filename, $matches);
            if (isset($matches[1])) {
                $source_locales[] = $matches[1];
            }
            
            // Copy if doesn't exist or is newer
            if (!file_exists($target_file) || filemtime($source_file) > filemtime($target_file)) {
                if (copy($source_file, $target_file)) {
                    $copied++;
                }
            }
        }
    }
    
    // Remove duplicates
    $source_locales = array_unique($source_locales);
    
    // PART 2: Delete files from target that don't exist in source
    $target_files = glob($target_dir . '/LayerSlider-*.{mo,po}', GLOB_BRACE);
    
    // Protected locales (never delete these - they're from the plugin itself)
    $protected_locales = ['en_US', 'fr_FR', 'hu_HU', 'uk'];
    
    if ($target_files) {
        foreach ($target_files as $target_file) {
            $filename = basename($target_file);
            
            // Extract locale from filename
            preg_match('/LayerSlider-([^\.]+)\./', $filename, $matches);
            if (!isset($matches[1])) {
                continue;
            }
            
            $locale = $matches[1];
            
            // Skip protected locales
            if (in_array($locale, $protected_locales)) {
                continue;
            }
            
            // If this locale is NOT in source directory, delete it from target
            if (!in_array($locale, $source_locales)) {
                if (unlink($target_file)) {
                    $deleted++;
                }
            }
        }
    }
    
    return ['copied' => $copied, 'deleted' => $deleted];
}

// 3. Helper function
function child_theme_get_available_languages($locales_dir) {
    $languages = [];
    
    if (!is_dir($locales_dir)) {
        return $languages;
    }
    
    $files = glob($locales_dir . '/LayerSlider-*.mo');
    
    if (!$files) {
        return $languages;
    }
    
    foreach ($files as $file) {
        $filename = basename($file, '.mo');
        $locale = str_replace('LayerSlider-', '', $filename);
        if (!empty($locale)) {
            $languages[] = $locale;
        }
    }
    
    return $languages;
}

// 4. Insert button in dashboard
function child_theme_layerslider_add_sync_button() {
	$screen = get_current_screen();
	if (!$screen || strpos($screen->id, 'layerslider') === false) {
	    return;
	}
	?>
	<script type="text/javascript">
	    jQuery(document).ready(function($) {
	        setTimeout(function() {
	            if ($('.ls-sync-languages-button').length > 0) {
	                return;
	            }
	            
	            var $settingsButton = $('.ls-open-plugin-settings-button');
	            
	            if ($settingsButton.length === 0) {
	                return;
	            }
	            
	            var syncUrl = <?php echo wp_json_encode(add_query_arg('ls_sync', '1', admin_url('admin.php?page=layerslider'))); ?>;
	            
	            var $syncButton = $('<a>', {
	                href: syncUrl,
	                class: 'ls-button ls-sync-languages-button',
	                html: '<?php echo addslashes(lsGetSVGIcon("globe")); ?>'
	            });
	               
	            $settingsButton.before($syncButton);
	            
	        }, 500);
	    });
	</script>
	    
	<style>
	.ls-sync-languages-button:hover {
	    color: #fff;
	    background: #54575f;
	    border-color: #0000;
	    transition: opacity 0.2s;
	}
	</style>
	<?php
}
add_action('admin_footer', 'child_theme_layerslider_add_sync_button');

// 5. MANUAL TRIGGER
function child_theme_layerslider_manual_sync() {
    if (!isset($_GET['ls_sync']) || $_GET['ls_sync'] != '1') {
        return;
    }
    
    if (!current_user_can('manage_options')) {
        wp_die('No permission');
    }
    
    $success = child_theme_patch_layerslider_template();
    
    $redirect_url = admin_url('admin.php?page=layerslider');
    
    if ($success !== false) {
        $redirect_url = wp_json_encode(add_query_arg('ls_synced', '1', $redirect_url));
    } else {
        $redirect_url = wp_json_encode(add_query_arg('ls_sync_failed', '1', $redirect_url));
    }
    
    wp_redirect($redirect_url);
    exit;
}
add_action('admin_init', 'child_theme_layerslider_manual_sync', 1);

// 6. AUTO-PATCH after plugin update
function child_theme_layerslider_after_update($upgrader_object, $options) {
    if ($options['action'] !== 'update' || $options['type'] !== 'plugin') {
        return;
    }
    
    if (!isset($options['plugins'])) {
        return;
    }
    
    foreach ($options['plugins'] as $plugin) {
        if (strpos($plugin, 'layerslider') !== false || strpos($plugin, 'LayerSlider') !== false) {
            // Run patch automatically after LayerSlider update
            child_theme_patch_layerslider_template();
            break;
        }
    }
}
add_action('upgrader_process_complete', 'child_theme_layerslider_after_update', 10, 2);