Markup Proposal taken from http://moinmo.in/ParserMarket/Abbreviation:

• ^WAI^ Marks the word WAI as an abbreviation and tries to retrieve the explanation from the standard abbreviation definitions page "AbbrDict"

• ^WAI|OtherPage^ Marks the word WAI as an abbreviation and tries to retrieve the explanation from the specified page "OtherPage".

• ^WAI:Web Accessibility Initiative^ Marks the word WAI as an abbreviation and uses the given explanation.

• ^WAI|language=de^, ^WAI|OtherPage|language=de^, ^WAI:Web Accessibility Initiative|language=de^ Marks the word WAI as an foreign language abbreviation (compared to the language default of the wiki and the page)

Since the <acronym> tag won't be probably part of future (X)HTML standards, only <abbr> is used in Moin to mark acronyms and abbreviations.