Fluid: TranslateViewHelper does only work once
The TranslateViewHelper does only work once. If you put more than one translate tag in your template only the first gets translated.
By looking at the code I think that it gets even worse. The TranslateViewHelper will only work once per HTTP request. That means that only the first translate tag of the first loaded extension will get translated and the following translate tags won't.
The problem seems to be the initialization check. The TranslateViewHelper will not get initialized after the first instance and therefore the member variable $this->LOCAL_LANG which holds the locallang information is empty.
I would suggest to create a LanguageRegistry (a Singleton) which holds the locallang information once per extension. Where should something like this be put? extbase or fluid?