Generaxion

Changing the WordPress site language to any other than English slows down page generation times. A lot. This is caused by the slow and inefficient way of text domain loading. This plugin, based on the excellent work by Björn Ahrens, aims to fix that by loading only the text domains that are used in a page and even more, by caching them. 
PO and MO files are designed to be used with PHP Gettext-extension. But since it\’s an extension, it\’s not installed by default on all hosting platforms. To overcome this barrier, WordPress has re-implemented the whole MO file parsing in PHP completely ignoring the possibility to use native gettext, if available. This WordPress\’ implementation is a bit slow. 
This plugin has another implementation of MO parsing, which is faster than the default one. The plugin also loads only the text domains that are required to generate the current page instead the default behavior of loading every available text domain. As front end pages usually only use strings from few text domains, this leads to a great performance boost in front end. 
To boost the performance even more, the plugin also caches the loaded text domains in to the object cache. For optimal performance you need a fast object cache backend like Redis, Memcached or APC(u).
<h4>Links</h4>
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<li><a href="https://github.com/aucor/dynamic-mo-loader" rel="nofollow ugc">GitHub</a></li>
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Dynamic MO Loader

Better text domain loading with object cache support

Tom Auger

This plugin, once activated, spits out the information passed by each filter used in manipulating database queries, as a learning tool.
The code itself is heavily documented and demonstrates best practices for working with those filters and actions to view / manipulate the query.
It is very important to note that this plugin is not meant for a production environment as it will insert a lot of really ugly HTML throughout your page. You’ll get the most use out of this plugin by looking at its code, and maybe previewing one or two pages on a sandbox, vanilla WordPress site.

Valz Display Query Filters

This demonstration plugin identifies the primary filters that are used by WordPress as it parses your queries.

Dynamic MO Loader vs Valz Display Query Filters