Hi Hippietrail!
What do you mean by "intractably slow"? Just how fast must it be?
If I do
http://en.wikipedia.org/w/api.php?action=query&list=embeddedin&eiti…
it says (on one given try) that it was served in 0,047 seconds. How
long can it take to read them all? A few minutes?
Seems to me that time would be swamped by the time it takes to pull
the wikitext for the pages?
And methinks you might be trying too hard to parse the text, some
fairly simple regex or such can extract the template invocation and
the parameters; people use it in a pretty regular way.
Oh, and do remember to look for "Template:Infobox language" as well,
depending on which way you find them.
Robert