For the language file, depending on what version you upgraded from, you may need to update/modify your language files. With the 3.2/3.3 releases, we had unified the Joomla 1.5 and Joomla 1.6 strings to be the same, which caused changing most of them. Either way, I'd check the german language file for both the component (xx_YY.com_jfbconnect.ini) and the login module (xx_YY.mod_jfbclogin.ini) against the English version to see if there are any strings missing. Sometimes on upgrades, we've seen that language files don't get overridden properly. It's also possible we missed a few strings when converting. If so, please feel free to contribute any language strings back to use for inclusion in the next release.
As for the parameters not working, I'm honestly not sure. Can you try some of the other parameters, like the "Show Powered By" link to see if that properly appears? Let us know, but there were no changes in 3.4 (that I can think of) that cause the logout button to always show.
Thanks,
Alex