Hailstorm

WCAG 1.0 Guideline 4: Clarify natural language usage. Content developers should provide expansions of abbreviations and acronyms.

Accessibility Abbreviation

Add abbreviation-tags via TinyMCE to comply with the Web Content Accessibility Guidelines.

Whodunit

Jb Audras

This plugin should be used to supply abbreviation support in the TinyMCE visual editor. Once activated, it provides an “ABR” button which allows editor to indicate the meaning of each abbreviation used in Pages, Posts or any custom post types used in your WordPress installation. The markup is fully compatible with accessibility rules like Web Content Accessibility Guidelines (WCAG). It uses <code><abbr>…</abbr></code> HTML markup instead of the deprecated <code><acronym>…</acronym></code> HTML markup.
Available languages
<ul>
<li>English</li>
<li>French</li>
</ul>
You can add your own language pack: contribute <a href="https://translate.wordpress.org/" rel="nofollow ugc">here</a>! Contributors will be linked back here. 
Search Plugins > Abbreviation button for tinymce and add your translations. Many strings are commented to help you to understand context.
Credits
<a href="https://jeanbaptisteaudras.com/" title="Jean-Baptiste Audras" rel="nofollow ugc">Jean-Baptiste Audras</a>, WordPress projects manager at <a href="http://www.whodunit.fr/" title="Whodunit Web Agency" rel="nofollow ugc">Whodunit</a> and WordPress developer. @audrasjb on <a href="https://twitter.com/audrasjb" title="@audrasjb on Twitter" rel="nofollow ugc">Twitter</a> or <a href="https://github.com/audrasjb" title="@audrasjb on Github" rel="nofollow ugc">Github</a>.

Abbreviation button for TinyMCE

Provides abbreviation button for WordPress TinyMCE visual editor.

Accessibility Abbreviation vs Abbreviation button for TinyMCE