Hi,

I'm not sure, if it is correct to write something like
"Mi eris en Aŭstrujo por du semajnoj"

Is this sentence correct?

Apart from "estis" ("mi eris" literally means, "I have been a particle"!), the correct preposition here is "dum" (="for the duration of"). Therefore you will say:

Mi estis en Aŭstrujo dum du semajnoj.

The preposition "por" means "in order to", "to the advantage of":

Mi faris tion por vi.
I did that for you.

Mi manĝis por travivi.
I ate (in order) to survive.

I usually agree with mnlg but his answer with relation to "por" is a little incomplete, I think. According to the PMEG, "por" can be used to indicate time in some specific cases.

This is a translation of the PMEG's discussion of "por" to indicate time:
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"Por" can show a desired length of time. It has to do with the time that an action should last, or with the time taken by the result of an action:

* Por momento ŝi silentiĝis.[M.123] = She was silent, and the silence lasted for a moment.

* Kuzino Marinjo! mi petas vin ĉi tien por unu minuto.[M.44]

* Li forveturis por unu tago pro tre grava afero.[Rz.90]

* Tie troviĝu almenaŭ nova freŝa funebra krepo, kiam la maljunulo fermos por ĉiam siajn okulojn.[FA3.146]

Don't confuse temporal "por" and "dum". "Dum" simply shows a length of time. "Por" shows a desired length of time. "Mi petas vin cxi tien dum unu minuto". The act of requesting lasts for one minute, in this example. "Mi petas vin cxi tien por unu minuto". The request means, that the person I am speaking to should come and stay for one minute.

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In this case, with relation to the sentence for Austria, my answer is the same as mnlg's. You were already in Austria, so it doesn't matter how much time you planned to be there; you were actually there for two weeks, so "dum" is the right word, and mnlg's correction is right.

If you wrote the sentence before the trip, though, you could say "Mi iros en Auxstrujo por du semajnoj", because that is the planned length of your trip (and the actual trip may or may not last two weeks, depending on whether everything goes according to plan). If you said "Mi iros en Austrujo dum du semajnoj", that would mean that the act of going to Austria will take you two whole weeks (a long time! Perhaps in that case, you'd be taking a train there from China!)

The idea in that use of "por" is, i think, to mean "mi iros por resti dum du semajnoj". I have always understood it like that and that's why I do not connect it to time duration directly. However, technically, it can look that way.

Actually, in cases like this some people just drop the pronoun and simply use an accusative. Which would give you:

Mi estis en Aŭstrujo du semajnojn.

It would help to know the reason for your being in Austria for this length of time. If you were on holiday or a conference which just happened to last two weeks, but it could have been longer or shorter, then dum might be more appropriate. But if you intended (or were intended) to make just this period of time available for an important purpose, then por might be more suitable. Por implies purpose!

Rogir:Actually, in cases like this some people just drop the pronoun and simply use an accusative. Which would give you:

Mi estis en Aŭstrujo du semajnojn.

I also prefer it this way