Sorry for not reposting a link directly to steps for this - Leo had actually already linked to the task that describes exactly what you ask for: that is, this topic that describes the steps necessary to make a selection into a single system. It includes a screenshot of the relevant button in the Formatting panel (the one on the left in Engrave mode). I’d seen that you’d said you already knew this after Leo posted a link to this topic, so I didn’t think it would be helpful to repost it, but perhaps I should have.
Yes I can see now that “Notenzeilnabstand” produces no results, but “Notenzeilenabstand” does in the manual.
“Notenabstand” also produces a number of relevant results.
And “Enharmonic” doesn’t come up in the German manual, but “enharmonisch” (as I remember you mentioning earlier) also has a number of relevant results.
There’s a really tough line to tread in documentation between providing all possible terms/spellings/words etc and keeping a manual’s terminology consistent. In the English manual, I try to include synonyms at least once so that users have a better opportunity to learn which term we use in Dorico, but it’s not always practical or possible for translators to do this too (due to different languages having different vocabularies).
When you’re searching, if it’s possible to try variations on your search, e.g. with fewer words, an alternative term, or a more generic version of a word, I’d recommend trying that. Or, if you feel comfortable, you can always switch the /de/ in the help url to /en/ and try searching the English manual (all topics have the same name in all manuals, just with the different language code, so you can switch between languages on the same page). When the next update to localised documentation is published for Dorico 3, there will be an increase in alternative phrases embedded in the metadata in various places, which might improve search results for a wider range of musical terms. I’ll use your suggestions to check this once the translations are returned, and if in the meantime you come across any other terms that could either be added or provide more results, please do add to this thread - I’ll keep an eye on it.