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.

Sergey Biryukov

webvitaly

karevn

Atrax

Converts Cyrillic and Georgian characters in post, page and term slugs to Latin characters. Useful for creating human-readable URLs.
This plugin is a fork of <a href="https://wordpress.org/plugins/cyr2lat/" rel="ugc">cyr2lat</a> plugin.
<h4>Features</h4>
<ul>
<li>Automatically converts existing post, page and term slugs on activation</li>
<li>Saves existing post and page permalinks integrity</li>
<li>Performs transliteration of attachment file names</li>
<li>Includes Russian, Belarusian, Ukrainian, Bulgarian and Macedonian characters</li>
<li>Transliteration table can be customized without editing the plugin itself</li>
</ul>
Based on the original Rus-To-Lat plugin by Anton Skorobogatov.

Cyr to Lat enhanced

Ин дид, зыс плагин конверт май линкс фром кириллик ту латин вэри фаст, изи, энд визаут эни ишьюс, сенк ю!

Воркс лайк э чарм!

Converts Cyrillic, European and Georgian characters in post, page and term slugs to Latin characters.

Bunny’s Language Linker vs Cyr to Lat enhanced