The new seasonal task in the tamriel tome bares a major translation error that will keep any german player that doesn't utilize the english localization of the game from ever finishing the new seasonal task.
The german version reads, directly translated into english, like this: "Finish 1.000 endeavours in a group"
Which has absolutely nothing to do with the actual task at hand: "Kill 1.000 Foes in the Gold Coast, Hew's Bane, or Wrothgar."
Now, you may have noticed that this is not only NOT the current new seasonal task, but also that endeavours are a thing of the past.
Wrong german version:

I only found out what I actually had to do to earn my 1.000 tome tokens because another german player, who happens to use the english client, informed me about the error.
Many others might not get that lucky and miss out.
Major edit: I made a similar post on the german forum and one of the moderators was so kind to explain what exactly happened here. So for anybody who's interested, here we go. I'll try to translate things:
The texts in ESO, for books and quests and even tome tasks, are stored in so called 'Strings'.
The game assigns IDs to each line of text we see displayed in our language ingame. To save some space, older strings that are no longer in use, will be simply overwritten with new ones.
This specific tome task holds the ID 'timed_320'. Up until february the task itself was indeed still 'Finish <<01*endeavours^f in a group'. The '01' is the variable that makes for the actual count of '1000'. The '^f' signales the grammar tool, that the word is simply female (For the german example) and therefore assignes the fitting pronoun. (Which might explain why it hit the french and russian, too. Because the french handle things similar to us germans and for some reason russia has both 'soft' and 'hard' pronouns. Why guys...)
Sadly, the english string got changed to the task we got today before the other localizations could receive the translated strings and so the patch hit the live servers with what we have now.
This is why the english client shows the correct tome task while the german, french, russian and possibly other players are left with the 'old' and therefore incorrect variant.
End of story: The translation is still handled by actual humans. Fantastic. But the patch got pushed out before they could quickly translate the last minute change made to the tome task.
Thanks to
@ZOS_KaiSchober for clearing that up.