The spell checker in Thunderbird, Firefox and SeaMonkey uses Dictionaries as the language pack is for the language of the user interface or UI.

https://support.mozilla.org/en-US/kb/how-install-and-use-another-language-dictionary-th

Ok,

I used the wrong wording "language pack", but see the error message (enclosed red) I got when I try to install the Dutch dictionary:

Best regards,

Jeroen

By the way it worked all fine before. I did not need this kind of version update.

Regards,

Jeroen

You should be able to install the dictionary if you change the preference extensions.strictCompatibility to false. Tools/Options/Advanced/General/Config. editor, double-click the preference to toggle it to false.

See the first 'Changed' item here:

https://www.thunderbird.net/en-US/thunderbird/60.0beta/releasenotes/