[TYPO3-dev] Value of dynamic name variable typoscript

[gal typo]

Hi
I defined a label in a locallang.xml file.

And I want to get dynamically his value, in a HMENU /TMENU/CUR, by doing an :
stdWrap.dataWrap = LLL:fileadmin/templates/language/locallang.xml:{field:subtitle}

Unfortunately, I get LLL:fileadmin/templates/language/locallang.xml:lib_mypage instead of the value on lib_mypage in locallang.xml
How to eval() an expression obtained by datawrap?

PS : 
- "subtilte" of a page is defined as a text (like "lib_mypage" )
- "lib_mypage" is defined as an label in "locallang.xml"

thanks