Learn Romanian: Am locuit aici timp de două luni.

In the Romanian past tense, the helping verb am is used for both 'I' (eu) and 'we' (noi). So, am locuit can mean either 'I lived' or 'we lived.' You usually tell which one it is from the context, or by adding eu or noi to the beginning of the sentence if it is ambiguous.

Why do we use timp de here to mean 'for'? Can I use pentru instead?

When you are talking about an enclosed duration of time (how long an action lasted), Romanian uses timp de (literally 'time of'). You should avoid using pentru, as pentru usually translates to 'for' in the sense of 'intended for' or 'on behalf of' (like buying a gift for someone), rather than for time duration.

Why is it două luni and not doi luni?

In Romanian, the number two changes based on the gender of the noun. The word for month, lună, is feminine. Because its plural form luni is still feminine, you must use the feminine form of two, which is două.

Doesn't the word luni also mean Monday?

Yes! luni is both the plural of lună (month) and the word for Monday. In sentences like this, the number right before it (două) makes it instantly clear that we are counting months, not talking about Mondays.