Those things are saved in the language files. You would need to "translate". However, LS is open source, so you can make suggestions to the translation. Just find the string and make a suggestion to change the translation, and see if it is approved or not. You can use the same credentials as for the forum to login:
translate.limesurvey.org/projects/limesurvey-3/
However, I just checked for the translation German-Informal and all strings with reference to "No answer" are capitalized ("Keine Antwort"). Checked for just "German" and you are right, it says "keine Antwort". It is a small inconsistency, but you can suggest it to be changed.
On the way I found a real grammatical error in one of the strings and corrected it. Hopefully it will be in the next release.
However, if you want full control over what your answer options are saying, don't use the "no answer" from Limesurvey, but create your own answer option "no answer", then you have total control over the text, its formatting and its translations.