how to notify regarding "404" errors
I am doing one of the "relationship" lessons where the task is to write in German "My mother and he are siblings."
I wanted to post the following into "Discussion": I answered "Meine Mutter und er sind geschwistern." and it marked that correct but said I have a typo and that the last word should be "Geschwister". Google Translate says that "Geschwister" means "brothers and sisters" and that "Geschwistern" means "siblings". Of course Google Translate isn't perfect, but I wonder whether its opinion has merit in this instance. Any opinions? (I hope my failure to capitalize "Geschwistern" isn't relevant here.)
However when I went to the "Discussion" tag there was a picture of a wounded Duo and "404" page not found indication. Purpose of this note is to bring attention to that broken link, and perhaps get advice on the above query.
I can only answer your German-language question:
"Meine Mutter und er sind Geschwister" is correct because in this sentence, the nominative case is required, and this is "Geschwister".
"Geschwistern" is dative case. For example, you could say: Dieses Buch gehört meinen Geschwistern. (This book belongs to my siblings). Since the verb "gehören" requires the dative case, the form "Geschwistern" is correct in this sentence.
First of all: Do you think there is any difference between "siblings" and "brothers and sisters"?
About how to use Google Translate: It does not only give you one transtation. Click on the line below the first translation and you will get other translations. In German there is written "2 weitere Übersetzungen" (2 other Translations). Then you will see, that "Geschwister" means both "siblings" and "brothers and sisters" as well. I do not know why google gives for "Geschwistern" only siblings.
About typos in Duolingo: For Duolingo a typo can only be a word that does not exist. If the wrong typed word exists aswell, Duolingo can't see the difference between a typo and a mistake.
About "Error 404": I hate it too. I don't know how it is produced or prevented.
Not sure why you got a 404 error - I can open the discussion page.
Generally, not all 404 errors are "fixable" by the course contributors... you can report it during the lesson (mention that you saw a 404 error for the discussion page), or even better file a bug report. The latter goes to the Duolingo staff, rather than the course contributors. They have more power to fix website issues.