I think "where were you for so long?" does sound more natural/normal than leaving the "for" out; however, even if the "for" is required to be strictly grammatically correct, the non-"for" version would make sense and be understood. I don't think the non-"for" version is as common though.
I'm a native UK English speaker, I'm sure there are people here using English as their second language to interpret this. I feel for them. I directly translated the phrase knowing the answer to make very little sense in English. I agree with other posts, we would say "where have you been for so long".
It sounds fine to me (native US), though I might opt for "Where were you for so long?"
Without knowing what sounds wrong to you about it, I'm not sure I can provide a translation that sounds better to you, but the meaning is essentially "You were gone for a long time. Where were you?"
-Copernicus-,zengator my question is the same as philippecm, since we are learning adjective endings in German, pls can anyone say why an e at the end of lang, there is no noun following lang, how do we use the rules for adjective endings, can someone pls help with the mysterious e in the lange.
"Lange" here is an adverb, not an adjective. Normally adverbs don't take any sort of ending at all, and actually just "lang" works fine here. Both "lang" and "lange" are completely equivalent when they're an adverb, and either one can be used for this sentence; I'm not sure of the reason for the "-e" on "lange" though.
Where is the "Accusative Case" in this Question? Where is "the what" in this question? If I use the other form of this question: 'Where have you been so long?", could I "force" an Accusative form by pointing to the presence of the "have" in this other form of the question as indicative of the Accusative presence?
There's simply no accusative case here. Only nouns and pronouns have cases, and the only noun/pronoun in this sentence is "ihr," which is of course nominative.
could I "force" an Accusative form by pointing to the presence of the "have" in this other form of the question as indicative of the Accusative presence?
No, the fact that the English sentence has "have" doesn't affect how the German sentence's grammar works. Even if it did, "have" is an auxiliary verb here and not the kind of "have" that would have a direct/accusative object.
A couple issues:
What has happened to you for so long?
Wo seid ihr so lange gewesen?
Wo is where and gewesen is have been, the overall emphasis being on where the person has been, not necessarily what happened to them. Although this may be implied by asking where they've been for so long.
The "for" can be dropped in colloquial speech and frequently is.
Well, now that I've learned more, I can correct my own error: it is Wo seid ihr and Wo seid Ihr is completely wrong.
Why? Because ihr is the plural second person (i.e., "y'all"). I have a bad habit of wanting to make it be the formal third person.
Ah, well . . . apparently ich lerne.
Sehr interessant. Hier ist ein kurze Diskussion: https://en.wikipedia.org/wiki/T%E2%80%93V_distinction#German
Auch kann man auf Seite 1673 f. von "Language History and Linguistic Modelling: A Festschrift for Jacek Fisiak on His 60th Birthday, Volume 1" (Hgg.: Raymond Hickey und Stanisław Puppel; Verlag: Walter de Gruyter, 1997) verweisen.