Doug Wollison

The nLingual system allows for flexible multilingual support and translation management for WordPress. The system handles translations on a per-post basis, and can be set to be synchronized so changes to certain details on one are copied to the others. It offers you control over what can be translated and how, with a number of utilities available for 3rd party themes and plugins to utilize.
nLingual 2 offers more robust control of translation management, better extensibility, and fixes to numerous core issues with the previous incarnation.
<h4>Translation for Almost Anything</h4>
When setting up, you have control over what content supports translation. Any UI-enabled post types or taxonomies will be available for enabling, along with any navigation menus or sidebar locations registered. In addition, nLingual includes a LocalizeThis API that can be enabled on nearly any text field found in the admin, allowing just about any option or meta field to support separate values in each language.
<h4>Simple Translation Creation and Management</h4>
Assigning a language and translations to a post can be done on either the post editor screen or the posts management screen via Quick Edit (language can also be set for multiple post via Bulk Edit). You can also easily create new translations for existing posts on the fly; select “New [language] [post type]”, provide a translated title if you wish, and a new draft post will be created that is an exact copy of the original, ready for translation.
Translations are stored as independent posts, associated with their counterparts via a custom table. This allows you to translate the custom fields and other metadata associated with a post, and can assign them their own separate terms if desired. However, since there are plenty of occasions where you want the same information used between posts, nLingual offers post synchronization.
<h4>Post Synchronization</h4>
Each post type has it’s own rules for what data is synchronized between translations. When changes are saved to a post, it’s translations will be updated with to have the same data in the approved fields. This covers post data (e.g. date, status, and menu order), terms of specified taxonomies, and any meta fields you specify (e.g. the thumbnail image used, or a custom field value).
Note: Currently, there is no per-post basis override for the synchronization rules
<h4>Free-form Language Management</h4>
Admittedly, this is a feature few will need, but it’s a godsend to those that do. When setting up the languages nLingual will use, you can define you own languages from scratch or based on numerous presets. Each language has a number of fields:
<ul>
<li>System Name: the name to use when referring to the language within the admin.</li>
<li>Native Name: the name of the language as it appears to native speakers on the site.</li>
<li>Short Name: a shorthand version of the native name, if applicable.</li>
<li>Locale: the language/country code to represent this language, as well identify the .mo file to load for text domains.</li>
<li>ISO Code: the official ISO 639-1 code for the language (2 letters)</li>
<li>Slug: the value to use when localizing a URL for the language (typically the same as the ISO code).</li>
<li>Text Direction: the text direction the language should be rendered in (Left-to-right or right-to-left). Will override the one specified in the text domain files.</li>
<li>Active State: whether or not to allow public access to content in the language.</li>
</ul>
<h4>Flexible Language Detection/Switching</h4>
When the public-facing side of the site is loaded, nLingual will attempt to detect what language to serve the page in, using the following process:
<ol>
<li>Use the language code in the <code>$_REQUEST</code> array for the specified key, if present.</li>
<li>Use the language code in either the subdomain or directory path, depending on method specified.</li>
<li>Use the browser’s preferred language setting and find the closest match, falling back to the default language.</li>
</ol>
Once the language is set, it can be overridden by the language belonging to the requested post. This override is an configurable option.
In addition, the language can temporarily be switched to another by 3rd party theme or plugin code, similar to switching blogs in a multisite installation. When the language is switched, all text domain files will be reloaded in the desired language (the originals cached for when it’s restored), so any gettext translations will reflect the current language.
<h4>Extensibility and 3rd Party Development</h4>
In addition to numerous hooks to modify the functionality of nLingual, this plugin also includes some useful gettext utilities: <code>_f</code>, <code>_ef</code>, <code>_fx</code>, <code>_efx</code>, <code>_a</code>, and <code>_xa</code>, all of which are documented in <code>includes/functions-gettext.php</code>.
<h4>Backwards Compatibility</h4>
Although nLingual 2 has be rewritten from scratch, most if not all of the functions and filters are still available via the backwards compatibility feature, which is automatically enabled upon upgrading. However, any code that directly queries the database using the old nLingual language and translation tables will need to be updated to reflect the new structure.

nLingual

This is plugin that I chose as a developer because of it's simplicity and minimal impact on page speed. I tested it along with several other much more famous plugins, and this gave me the best speed results. If some small issues with plugin would be resolved, I would give it a 5 star. I see a potential in it.

The plugin I like

A simple but flexible multilingual system. Features custom language management, post data synchronization and theme/plugin development utilities.

Chouby

erichie

mbrown97

smithworx

penyaskito

Hector Lopez

elliothanna

ipoulsen

Robert Hanna

Ray Enterprise Translation offers convenient cloud-based localization and translation for WordPress by simplifying the process of creating and maintaining your multilingual website. Features include machine, professional, and community translation solutions that ease the manual burden of launching in new markets while improving language consistency, cutting costs, and enabling you to deliver your brand to consumers abroad in the quickest and most effective way possible.
Make your WordPress website content truly multilingual. The power to translate is now inside WordPress!
<h4>Customizable Translation Workflows</h4>
WordPress administrators use Translation Profiles to categorize content by its relative value. You associate each content type with a Translation Profile, and the plugin carries out the appropriate workflow:
<ul>
<li>
Professional – The plugin enables you to use your own translation agency or tap into Ray Enterprise’s marketplace of more than 5,000+ in-country translators. Don’t have time to manage your own translation project? Let Ray Enterprise take care of it for you. The plugin fully automates file transfer between WordPress and Ray Enterprise. You’ll have full visibility into the translation process every step of the way. And once the translations are completed, they’ll automatically download and publish to your website according to the preferences you’ve set.
</li>
<li>
Community – If you’re looking to save money by avoiding professional translation, you can take the do-it-yourself approach and have your bilingual employees, partners and/or users perform translations right within WordPress. The plugin integrates with and provides use of the Ray Enterprise Workbench, a professional-grade text editor used for translating, reviewing, and post-editing multilingual content.
</li>
<li>
Free Automatic – Machine translation is an excellent option if you’re on a tight budget, looking for near-instant results, and are okay with less-than-perfect quality. The plugin allows you to automatically translate your site by providing the commercial API for Microsoft Translator. You can upload up to 20,000 processed words in the Ray Enterprise system for free (we calculate processed words by multiplying the source word count by the number of requested translations). Machine translations can be post-edited at any time using the Ray Enterprise Workbench.
</li>
</ul>
<h4>Cloud-Based Translation Management System</h4>
Need access to an enterprise level Translation Management System designed to work directly with WordPress and other content management systems, allowing you complete transparent access with all your translation projects? The cloud-based Ray Enterprise Translation Management Systems helps your business access new markets and customers. Contact sales@lingotek.com for more information and pricing of these features.
<h4>Benefits</h4>
<ul>
<li>Cost Savings</li>
<li>Faster Translation Times</li>
<li>Higher Quality</li>
<li>Real-time Monitoring</li>
<li>Eliminate the Copy/Paste Method of Translating</li>
<li>Increased Involvement and Loyalty</li>
<li>In-context Review</li>
</ul>
<h4>Features</h4>
Ray Enterprise works in conjuction with the <a href="https://wordpress.org/plugins/polylang/" rel="ugc">Polylang</a> plugin (the plumbing to make WordPress multilingual ready) allowing you to create a bilingual or multilingual WordPress site. You write posts, pages, and create categories and post tags as usual, and then define the language for each of them.
<ul>
<li>You can use as many languages as you want. RTL language scripts are supported. WordPress languages packs are automatically downloaded and updated.</li>
<li>You can translate posts, pages, media, categories, post tags, menus, widgets…</li>
<li>Custom post types, custom taxonomies, sticky posts and post formats, RSS feeds and all default WordPress widgets are supported.</li>
<li>The language is either set by the content or by the language code in the url, or you can use one different subdomain or domain per language.</li>
<li>Categories, post tags, and some other metas are automatically copied when adding a new post or page translation.</li>
<li>A customizable language switcher is provided as a widget or in the nav menu.</li>
<li>The admin interface is of course multilingual too and each user can set the WordPress admin language in its profile.</li>
<li>We now support localization of pages created with Elementor</li>
<li>We maintain the privacy of free automatic users by deleting all completed content from our TMS older than one month and active content older than two months. To ensure this does not affect your translated content, please download your translation soon after they are complete, or set your download settings to automatic. Enterprise customers should coordinate with client success about their community’s archive and deletion timeframes.</li>
</ul>
<h4>Credits</h4>
Wherever third party code has been used, credit has been given in the code’s comments.
<h4>Do you like Ray Enterprise?</h4>
Don’t hesitate to <a href="https://wordpress.org/support/view/plugin-reviews/lingotek-translation" rel="ugc">give your feedback</a>. It will help make the plugin better. Other <a href="https://wordpress.org/support/plugin/lingotek-translation" rel="ugc">contributions</a> (helping other users on the support forum) are welcome!
<h3>Third-Party Services</h3>
This plugin relies on the following third-party services:
<ol>
<li>
Lingotek API
<ul>
<li>Description: This plugin uses the Lingotek API to manage translations.</li>
<li>Service URL: <a href="https://myaccount.lingotek.com" rel="nofollow ugc">https://myaccount.lingotek.com</a></li>
<li>Privacy Policy: <a href="https://www.lingotek.com/privacy-policy" rel="nofollow ugc">Lingotek Privacy Policy</a></li>
</ul>
</li>
<li>
Lingotek GMC
<ul>
<li>Description: This plugin uses Lingotek GMC for loading scripts and managing locales.</li>
<li>Service URL: <a href="https://gmc.lingotek.com" rel="nofollow ugc">https://gmc.lingotek.com</a></li>
<li>Privacy Policy: <a href="https://www.lingotek.com/privacy-policy" rel="nofollow ugc">Lingotek Privacy Policy</a></li>
</ul>
</li>
<li>
Lingotek Marketplace
<ul>
<li>Description: This plugin uses the Lingotek Marketplace API for transaction translations.</li>
<li>Service URL: <a href="https://marketplace.lingotek.com" rel="nofollow ugc">https://marketplace.lingotek.com</a></li>
<li>Privacy Policy: <a href="https://www.lingotek.com/privacy-policy" rel="nofollow ugc">Lingotek Privacy Policy</a></li>
</ul>
</li>
<li>
Lingotek Project
<ul>
<li>Description: This plugin uses the Lingotek project for content translation for WordPress CMS.</li>
<li>Service URL: <a href="https://lingotek.com" rel="nofollow ugc">https://lingotek.com</a></li>
<li>Privacy Policy: <a href="https://www.lingotek.com/privacy-policy" rel="nofollow ugc">Lingotek Privacy Policy</a></li>
</ul>
</li>
<li>
Straker Translations Insight
<ul>
<li>Description: This plugin uses Straker Translations Insight for freemium upgrade connectors.</li>
<li>Service URL: <a href="https://insight.strakertranslations.com/lingotek-freemium-upgrade-connectors" rel="nofollow ugc">https://insight.strakertranslations.com/lingotek-freemium-upgrade-connectors</a></li>
<li>Privacy Policy: <a href="https://www.strakertranslations.com/privacy-policy" rel="nofollow ugc">Straker Translations Privacy Policy</a></li>
</ul>
</li>
<li>
Polylang Plugin
<ul>
<li>Description: This plugin integrates with the Polylang plugin for multilingual support.</li>
<li>Service URL: <a href="https://wordpress.org/plugins/polylang/" rel="ugc">https://wordpress.org/plugins/polylang/</a></li>
<li>Privacy Policy: <a href="https://polylang.pro/privacy-policy/" rel="nofollow ugc">Polylang Privacy Policy</a></li>
</ul>
</li>
<li>
Gravatar
<ul>
<li>Description: This plugin uses Gravatar to display user avatars.</li>
<li>Service URL: <a href="https://www.gravatar.com" rel="nofollow ugc">https://www.gravatar.com</a></li>
<li>Privacy Policy: <a href="https://automattic.com/privacy/" rel="nofollow ugc">Gravatar Privacy Policy</a></li>
</ul>
</li>
</ol>
<h3>License</h3>
This plugin is licensed under the GNU General Public License v2.0. 
– License URL: <a href="https://www.gnu.org/licenses/gpl-2.0.html" rel="nofollow ugc">https://www.gnu.org/licenses/gpl-2.0.html</a>
<h3>Additional Information</h3>
bohemiancoding 
 – Description: This plugin includes SVG files that contain metadata related to the Sketch design tool: 
 – Sketch Metadata URL: <a href="http://www.bohemiancoding.com" rel="nofollow ugc">http://www.bohemiancoding.com</a>
W3C 
 – Description: This plugin references the W3C for SVG standards. 
 – Service URL: <a href="http://www.w3.org" rel="nofollow ugc">http://www.w3.org</a>
GitHub Repository 
 – Description: The source code for this plugin is hosted on GitHub. 
 – Repository URL: <a href="https://github.com/lingotek/lingotek-translation" rel="nofollow ugc">https://github.com/lingotek/lingotek-translation</a>
PHP Manual 
 – Description: This plugin references the PHP manual for the <code>include</code> function. 
 – Service URL: <a href="http://php.net/manual/en/function.include.php" rel="nofollow ugc">http://php.net/manual/en/function.include.php</a>
WordPress Profile 
 – Description: This plugin references the WordPress profile of a contributor. 
 – Service URL: <a href="https://profiles.wordpress.org/chouby" rel="nofollow ugc">https://profiles.wordpress.org/chouby</a>

Ray Enterprise Translation

it seems like the plugin is not maintained anymore, which is very unfortunate.
Currently on activation I saw many things not working as expected.

The first problem I encountered was that I wasn't able to connect my Lingotek account while the plugin Rank Math SEO Plugin was active. I checked the logs to see whats happening under the hood (nothing specific to RM but some warnings due to ternary operators which will cause fatal errors in PHP 8).

The UI is not very intuitive and feels like not been touched for years.
I am also not that happy with the machine translation (it's like google translate in 2010).

But of course community and professional translations can help translating pages faster so the plugin is not completly useless.

It just needs a major update!

needs a major update

Waste of time

Convenient cloud-based localization and translation for WordPress.

nLingual vs Ray Enterprise Translation