[TYPO3-mvc] fluid: inline translate with problems

[Johannes C. Schulz - EnzephaloN IT-Solutions]

Dear MVC-Comunity,

today a absolutely new problem appears. I use inline-translate to switch
between two icons:

<img
src="typo3conf/ext/enz_hotellist/Resources/Public/Icons/{f:translate(key:'bt
n_detail')}" border="0" alt="Detail" title="Detail">

The locallang.xml has values for "default" and for "de". If I visit the
german page all icons are displayed, but if I visit the english page no icon
is displayed.
Are there any changes between fluid of typo3 4.5.5 and 4.5.7 or what could
be the problem?

Thanks

Johannes