Not all strings translated

hi there
i just discovered this plugin which so far i think is great. i got one minor issue: two strings are not being translated into german. it is not the same problem as mentioned here and here, as i had german set as my language before the plugin-installation.
Here you’ll find the petition (scroll to bottom).
If you click on “Lesen Sie die Petition” (=read the petition), on the bottom of the pop-up appears (signature) instead of the german expression.
Same with the text that indicates the number of signatures (beneath the orange button): it says x signatures.
so it seems to me that the string “signature” has not been translated yet. how can i manage this? what file(s) do i have to manipulate?
Any help will be appreciated.

regards,

markus

https://wordpress.org/plugins/speakup-email-petitions/