[TYPO3-english] can't modify locallang.xlf from backend

[Matyi Gábor]

I'd like to modify some localization in the backend area, but I can't edit
the file locallang.xlf belongs to an extension.
In the extension manager I click on an extension, and after I click on the
files tab. Here I can modify every file, but I can't edit locallang.xlf,
hu.locallang.xlf etc.)

Do anybody has any idea how could I modify these localization files from
backend?

I use typo3 4.7