TYPO3 Core

all extension have this problem, both ext and sysext. the I make a example of tt_news, then you can understand well.
first I have write and save the ts that 'config.language = ch'

BUG show：
when yong de language packs in typo3. example with "root/typo3conf/l10n/ch" and "tt_news". If the document "root/typo3conf/ext/tt_news/pi/locallang.xml" have the code

<languageKey index="ch" type="array">
    </languageKey>

however I have translated the "root/typo3conf/l10n/ch" well. the document is "root/typo3conf/l10n/ch/tt-news/pi/cn.locallang.xml", the typo3 system used language "default".

when used the II-XMLtranslation Extension, the FE show good, because II_XML del the code " <languageKey index="ch" type="array"></languageKey>" of "root/typo3conf/ext/tt_news/pi/locallang.xml". This time the document "root/typo3conf/ext/tt_news/pi/locallang.xml" is changed. when I copy "root/typo3conf/l10n/ch" and give another one. His typo3 will not work in "ch" language.

In fact, when the variable "ch" of "root/typo3conf/ext/tt_news/pi/locallang.xml" like that, " <languageKey index="ch" type="array"></languageKey>" , the typo3 should to seach "root/typo3conf/l10n/ch" , but now typo3 not work as this.

the bug document is class.t3lib_div.php

(issue imported from #M6044)