[Typo3] Can someone explain this strange behavior

[Martin Kindler]

I am trying to add a local parameter to my menu items (in fact just to those
of type "External URL", but this will be
handled later :-))

I now have the following code, which works

temp.cxpmenu1.1.NO {
  doNotLinkIt =1
  before.data = field:uid
  before.wrap = <a href="index.php?id=|
  stdWrap.data = config.language
  stdWrap.ifEmpty < config.language
  stdWrap.wrap =  &locale=|" style="font-size:10pt;" >
  after.data = field:title
  after.wrap = |</a>
}

BUT: why does it NOT work to simply set the stdWrap.data to config.language.
Instead, it seems to clear the content (and then
the ifEmpty works.

I tried a lot of variants to set the content of the stdWrap to the value of
config.language but up to now the above variant is the only working
solution.

Martin