Steph

This plugin assumes you have a site in two or more languages, and that you are using a separate WordPress install for each language. It helps you create links between the same pages in different 
language versions.
You should have a pattern of parallel sites with urls like http://stephanie-booth.com/en/, http://stephanie-booth.com/de/, http://stephanie-booth.com/fr/. Maybe the page 
http://stephanie-booth.com/en/about is equivalent to the page http://stephanie-booth.com/fr/a-propos. The plugin adds a DBX box in the edit/create page admin form, named “Other Language Slugs”. In 
this case, you’d edit the “about” page, and paste the fr slug (“a-propos”) in the appropriate field.
The plugin will then display a small link to the page in the other language at the bottom of your page, or in your menu bar if you’re using a Sandbox-based theme.
Careful! This only works for Pages, not posts!
For intelligent user redirection when they land on the home page, you might want to try using the technique described here: http://climbtothestars.org/archives/2007/12/28/browser-language-detection-and-redirection/
<h3>Future Development</h3>
Here’s what I’d like this plugin to do, someday:
<ul>
<li>automatically capture URLs like http://stephanie-booth.com/en/a-propos and redirect them to http://stephanie-booth.com/en/about (that’s what happens when people edit URLs directly, just replacing 
the language code — I do it all the time)</li>
</ul>

Bunny’s Language Linker

Helps you create links between equivalent (but different language) pages between WordPress installations.

vivcheung

Frenglish provides a seamless way to translate your WordPress content into multiple languages. It integrates with your existing WordPress setup and provides an intuitive interface for managing translations.
Key Features:
<ul>
<li>Automatic language detection</li>
<li>URL-based language switching</li>
<li>Support for multiple languages</li>
<li>Easy-to-use admin interface</li>
<li>SEO-friendly URLs</li>
<li>Compatible with most WordPress themes</li>
</ul>
<h3>Privacy Policy</h3>
Frenglish uses an external API service for translations. Visit frenglish.ai for additional information

Frenglish Translations

Frenglish is a translation plugin that enables multilingual content on your WordPress site with an easy-to-use interface.

Bunny’s Language Linker vs Frenglish Translations