"Shall we go to the movie theater next month?"
In this section, whether or not there should be a は or a comma (、) after 来[week/month] seems to be completely random and subject to scrutiny if the "wrong" one is used, or am I missing a rule here?
On another note, could someone tell me if - and if so - the reason that this is incorrect? 「来月、映画館と一緒に行きましょうか」
P.S. this is just a silly idea of mine, but please consider maybe using an alternative for the word "theater", as I find it woefully easy to mix up with "together", and it makes for many annoying stupid mistakes.
the first is a state-blank polite soft invitation to which the listener has a right to decline.
The second one is used when the speaker is assuming the listener knows about this already, the assumption is not always true but ましょうか sounds more assertive to me because of this very same reason.
For example, you use ～ませんか to invite someone somewhere out of the blue, and then you use ～ましょうか to decide where you guys are going after receiving the "yes" for that initial invitation. Does that makes sense?
it is grammatical but is not as natural as using に。One of the reason is that you are making an assertive invitation with ～ましょうか which means you have a destination in mind. The other one is usage, natives tend to prefer に over へ unless there is a reason for it, like avoiding double particles or circumventing the problem of not being able to use に before a nominalizer like の、or maybe just placing emphasis on the direction you are going instead of the destination.