If you can write your posts in 2 or more(Woo…) languages within one blog, you might want to tell the client browser the language attribute of you posts.
According to <a href="http://www.w3.org/International/tutorials/language-decl/en/all.html" title=" W3C tutorial" rel="nofollow ugc">the tutorial on W3C</a>, language attribute can be declared in the container html tag of your post like this: 
<div id=”post_id” class=”post_entry” lang=”zh-Hant” xml:lang=”zh-Hant” dir=”ttb”>… 
Here “zh-Hans” is the language attribute of your post which means it’s written in Simplified Chinese.
This plugin gives your post a language tag by adding a meta deta to that post.
To add language tag, select it from the language box when you compose/edit a post. Select “None” will delete the language tag.
<h3>Revisions</h3>
2007-12-18, 
0.2: Now you can difine language direction. 
 Insert CSS style into page head automatically to support pretty printing.
 readme file updated for new feature and fixed a error
2007-07-23 
0.1: First release

Multilingual post

This plugin adds a standard compliant language tag to your post and page.

edo888

Google Language Translator plugin is now a part of GTranslate family!
GTranslate is a leading website translation services provider since 2008 and powers more than 500.000 multilingual websites worldwide.
Please use <a href="https://wordpress.org/support/plugin/google-language-translator/" rel="ugc">Google Language Translator Support</a> for your questions and support requests! We are multilingual!
Please check our <a href="https://gtranslate.io/?xyz=3167#faq" rel="nofollow ugc">FAQ</a> to get quick answers.
Features
<ul>
<li>Free Google automatic machine translation</li>
<li>Option to hide “Suggest better translation” pop-up</li>
<li>Option to hide Google top frame after translation</li>
<li>Google Analytics integration</li>
<li>Translate the site on the fly</li>
<li>Translate posts and pages</li>
<li>Translate categories and tags</li>
<li>Translate menus and widgets</li>
<li>Translate themes and plugins</li>
<li>Right to left language support</li>
<li>Floating language selector</li>
<li>Language bar with flags in menu</li>
<li>Translate WooCommerce shop</li>
</ul>
Paid Features
<ul>
<li>Multilingual SEO – Enable search engine indexing</li>
<li>Neural machine translations with human level translation quality</li>
<li>Increase traffic and AdSense revenue</li>
<li>Search engine friendly (SEF) URLs</li>
<li>Yoast SEO compatible</li>
<li>WooCommerce compatible</li>
<li>You can have sub-directory (example.com/es/) or sub-domain (es.example.com) URL structure</li>
<li>Translate URLs aka slug translation is possible (example.com/about-us → example.es/sobre-nosotros)</li>
<li>Add hreflang tags for translated alternatives</li>
<li>You can manually correct translations</li>
<li>In context translation interface (make corrections without losing the context)</li>
<li>Translate meta data (meta keywords, meta description)</li>
<li>Translating schema.org microdata for better search engine appearance</li>
<li>Seamless updates (cloud service updated on our side – SaaS, you do not need to worry about backups on your side)</li>
<li>Translate JSON objects (JSON format translation)</li>
<li>Translate AMP pages (Accelerated Mobile Pages translation)</li>
<li>Image localization – Translate media</li>
<li>Translation Proxy (aka Translation Delivery Network)</li>
<li>Centralized Translation Cache – We revise and improve translations over time</li>
<li>Language Hosting (example.fr)</li>
<li>User Dashboard with Analytics</li>
<li>Live Chat Support</li>
</ul>

Translate WordPress – Google Language Translator

When I use the shortcode in two places, the first is loaded but the second is not. (language switcher)

Use the short code in two different places


I never used a different Google Translator but with Google Language Translator there's really no need to. I'm very thankful to have this plugin installed not only for WordPress pages to get translated into the user's preferred language, but I also like to use it to translate text when I'm speaking with someone outside the us. After creating a test page in WordPress, I simply copy and paste the text that needs to be translated, hit the preview button and choose the language and my text instantly gets translated. 


Excellent


This is an outstanding plugin, and I've been using it for a few years now. My site is well-indexed and gets traffic to my language subdomains. However, it needs optimized better:1. The scripts.js doesn't need to be loaded if you're not offering a translation widget or shortcode on the front-end.2. The scripts.js has a toolbar.js code in it that's legacy and takes a hit from pagespeed.3. Hiding the flags div just adds a display:none div with all the flags in it.4. No hreflang tags are loaded in your header and no XML sitemap is generated to redirect for language.I've fixed all of these in my site, but it would be nice if these got corrected in the core code. I'd be glad to offer my code to assist.


Hide Language Switcher is display:none

Translate WordPress with Google Language Translator multilanguage plugin which allows to insert Google Translate widget anywhere on your website.

Multilingual post vs Translate WordPress – Google Language Translator