>> <acronym>-Tag, some web browsers doesn't show the user a visual
>> label like a dotted underline. If is a language-Attribute in the
>> <acronym>-Tag, like <span lang="de"> some browsers doesn't show
>> the titel from the <acronym>-Tag. 

> I didn't understant this.  The lang attribute is on the span, not the
> acronym opening tag, in your example.  I assume the mis-spelling of
> title is not present in the actual HTML.  (I read off line, so don't
> know what any referenced HTML document says.)

I will explain the problem with the <acronym>-Tag:

<acronym lang="en" title="Web Accessibility Initiative">
  <span lang="de">WAI</span>
</acronym>

First the language-Attribute within the <acronym>-Tag tell that the
title should in english, but after that the <span>-Tag switch the
language to german for the <acronym>.

Tested with Opera 8.50, now Opera doesn't display the tooltip with
"Web Accessibility Initiative". 

If i remove the <span>-Tag in this constellation then Opera will
display the tooltip again. 

And the tested screenreader from my visitor also doesn't switch the
language, all is read in english.