Translation does not work
I found one additionals thing: The translation does not work. I have a german environment, generally the extensions use the de.locallang.xlf. Sadly not this extension. I can not find any syntax problems in your de.locallang.xlf but it even does not show the german translation after I cleard all caches in the install tool. I also checked the installtool: [SYS][systemLocale] = de_DE ist set correctly.
Thanks and bye
Updated by Joerg Kummer about 3 years ago
I can confirm this behavior (TYPO3 8.7.12 pw_comments 4.0.0)
The loaded translation files from Translationsserver has empty <target/> values.
Until it is solved at translation server, a workaround for frontend is, to override locallang, using site-package extensions.
$GLOBALS['TYPO3_CONF_VARS']['SYS']['locallangXMLOverride']['EXT:pw_comments/Resources/Private/Language/locallang.xlf'] = 'EXT:my_sitepackage_extension/Resources/Private/Extension/PwComments/Language/locallang.xlf';