"We sometimes forget about the lunch."
Translation:Czasem zapominamy o obiedzie.
in Polish you don't have to change the "o" to "ob" when it's followed by a vowel (like you do in Russian)?
We do not change it. We add "e" to some words when they are followed by a group of consonants, for example: "w Warszawie" but "we Wrocławiu"; "przed tobą" but "przede mną".
There is no need for 'the' in this sentence. It is a mistake in English!
There is no need, but it sure is correct when it's some specific lunch. And versions without 'the' are accepted.
No, you cannot assume a specified lunch when the source is unspecific. Nouns only become soecified when they can be deduced as a property of something else, or if we directly specify it. One of the most difficult things about such a course with no storyline is trying to guess some random decisions by the course creator. Therefore, the use of 'the' here merely further undermines confidence in the course.
OK, with "sometimes", the 'specific lunch' interpretation indeed doesn't make much sense. I changed the main answer to just use "lunch".