Harry Fuecks at SitePoint - US-ASCII transliterations of Unicode text:
"[I] ported Text::Unidecode to PHP. [...] What I’ve done is easy, compared to the amazing job Sean M. Burke has done with Text::Unidecode. You really need to read the docs to understand what it does and it’s limitations but, in short, it keeps a “database” of unicode characters and corresponding sensible US-ASCII equivalents. For example, a simple transformation would be “Zürich” to “Zuerich”, “ue” being a common replacement for “ü” in Germanic languages."