Installed wrong language pack

[goliath]

Just installed guestbook 3.0 (for Joomla 3).
As it was installed in English, I tried to install the Dutch language pack. It installs fine but I think it was the translation for an earlier version of the guestbook. Most strings and buttons were untranslated and showed very weird texts. So I wanted to uninstall this language pack but now I receive very strange messages:

Warning
Package Uninstall: Missing manifest file

Message
Error uninstalling package.

Message
A language should always have been installed as a package.
To uninstall a language, filter type by package and uninstall the package.

How can I (manually) uninstall these language packs?

And is there a correct Dutch translation for version 3.0?

[Jan]

Hi, check if your language is up-to-date and see:

https://www.phoca.cz/documents/46-transl ... -in-joomla
Jan