[TYPO3-english] Problems with locallang.xml translation since 4.6

[Sören Kracker]

I can't get any other translations than default and de in 4.6. This all 
worked in 4.5!
This is really strange, because the content gets translated correctly 
(so language is set properly), but translations using locallang.xml 
don't work. Neither locallang of extensions (formhandler or overriding 
via $GLOBALS['TYPO3_CONF_VARS']['SYS']['locallangXMLOverride'] ) nor 
translations via typoscript (using LLL:translation.xml:string) are 
working. TYPO3 finds the xml files and fetches default strings and those 
for de too, but for en I always get the default translation.
Is there any change regarding XLIFF? I have absolutely no idea what's 
wrong here.

I have this setting for language config and English:
config {
     sys_language_overlay = hideNonTranslated
     sys_language_mode = content_fallback
     linkVars = L
}
[globalVar = GP:L = 1]
config {
     sys_language_uid = 1
     language = en
     locale_all = en_GB
     htmlTag_langKey = en
}
[global]

Simplified xml file (for formhandler):
<?xml version="1.0" encoding="utf-8" standalone="yes" ?>
<T3locallang>
<meta type="array">
<type>module</type>
<description>Language labels for plugin tx_formhandler</description>
</meta>
<data type="array">
<languageKey index="default" type="array">
<label index="reset">Zurücksetzen</label>
</languageKey>
<languageKey index="en" type="array">
<label index="reset">Reset</label>
</languageKey>
<languageKey index="en" type="array">
<label index="reset">Reset</label>
</languageKey>
</data>
</T3locallang>

Thanks for your help in advance

Sören