I do not have access to my poEdit right now, but here is what I recall. As I wrote, the culprit is in single.php line 26: the string is "% Comments".
- Open the po file
- Define the plural forms (although this is not the problem in this case
- Define language as Danish (although I doubt this makes any difference
- Make sure that poEdit is set up to automatically generate .mo file when saving in Options > Editor (or Editing or something like that - I can't see the English menu title)
- Search for the string "% Comments"
- Translate it to "% kommentarer"
- Save the file
- Now you see the error message I quoted in the initial message above
A proper solution would be to change the source to "%d comments", which means that the variable will be treated as an integer (which it is) and presented as a decimal number, signed if need be (which of course is not relevant here). See http://php.net/sprintf.
When poEdit parses "% kommentarer" in the Danish translation, it correctly objects that 'k' is not a valid conversion specifier. The space is ignored. Therefore, don't use '%' as a variable/conversion specifier, but use '%d', '%s' or one of the other valid specifiers.
Hope this makes it more clear.
Thank you, and a merry Christmas and a happy new year.