are you sure the translation file you are using is 100% complete?

Yes

I downloaded all the Po files from your site(theme, simple-press admin area, simple-press front-end) and opened them with the po-editor, but there is no such string(View listing of topics with new posts) for translation.

according to the code, it should be in the theme translation file… but not sure that is possible since the string is in core…  I suspect the translation function used there is the wrong one…  It should be changed to get from the core front end translation file…

if I am understanding this right…  @yellow-swordfish does our translation work… he will be out today and hopefully back tomorrow and will check with him…

if I have it right, we will have to get it fixed up in the 5.8 version we are working… 

thanks

I checked all translation files but there was no such string.

Location of the string: simple-pressforumcontentsp-common-view-functions.php

$out .= sp_UnreadPostsLink("tagId=spUnreadPostsInfo&tagClass=$tagClass&popup=1&echo=0&first=1&id=".$spThisForum->forum_id."&targetaction=forum", $flagstext, __sp('View listing of topics with new posts'), $spThisForum->forum_name);

Thanks for the updates.

that’s what I said…  would require us changing core to put it in a different translation textdomain…   until  that happens, it wont appear in any translation file…

yes, except it appears twice in that file you reference…