I was wondering about this for a while and I think on the Duolingo forums I saw a discussion about marking days of the week with the week, so like 来週の月曜日. Wondering whether that might sound more natural?
Stuff like that comes up on the news often so I’ll try to keep my ears peeled!
No clue whether there is a significant difference between つもり and ことにする, but the latter would be another option.
I pulled 次の月曜日 off Hinative, but the questions there tend to be entirely devoid of context so they might not always be the most natural options.
I think Monday might just be an example where it doesn’t really matter which you use since next Monday is always next week’s Monday (unless you’re a monster and you start your weeks on Sunday), but for other days it makes a lot of sense to make a distinction. After all, on Monday, 次の火曜日 and 来週の火曜日 are a week apart.
The way I understand them, つもり is about what you plan to do, while ことにする (or rather just にする - no idea why these are treated as two separate things) is about what you decide to do.
So there are situations where you could use both - if you decide to go somewhere tomorrow, you can say 明日は行くつもりだ or 明日は行くことにする. I feel like つもり emphasises the plan itself, and にする emphasises the decision you made.
However, にする is always about decisions you made, as I understand it, so if someone else made plans for you, you wouldn’t use it.
And likewise, when something isn’t so much about something you have planned but more just about a decision you make, it would feel a bit weird to use つもり. You could say 魚を食べるつもりだ in a restaurant, but 魚にする feels a lot more natural to me for saying you’ll have the fish.
In this particular situation, I think つもり might be a bit more natural, since the key element here (as I see it) is not the decision to go to the airport, but rather that going to the airport was planned at all, regardless of who made that decision.
Hopefully that was comprehensible. I’ve delayed output for much too long, so I’m wanting to take my first baby steps into output. This seems like a decent place to start! Feedback is always welcome!
で vs に has been the particle pair I struggle with the most, I feel. I never really know when it feels to right to use one versus the other. Thank you for the feedback!
They each have a fair few use cases which overlap sometimes, mostly when referring to locations in relation to the verb.
As a general rule, で refers to where an action takes place, and に refers to what the destination is for an action.
So 公園に歩く = to walk to the park, whereas 公園で歩く is to walk in the park, basically.
This can sometimes get a bit confusing in translation: 東京で家を書いた and 東京に家を書いた both mean “I bought a house in Tokyo”, but with で the nuance is you bought a house while you were in Tokyo, whereas with に it’s the house that’s in Tokyo, but you might as well have been in Brazil when you bought it.
I think in this case 公園を歩く might work a little better for “walk in the park”, because walking and the park are still linked. With で, walking is independent from the park and the park becomes more of a background context.
I think it would be 東京にある家を買った。With に alone we still have only 1 verb.
I did some extra searching for the 東京にアパート and came up with options which I think are a little clearer:
東京の賃貸アパート
東京の賃貸マンション
I would say that if it’s “an apartment in Tokyo” (and the reader/listener is not necessarily in Tokyo), 東京のアパート makes more sense. But I also don’t see any other response in the StackExchange thread to this and couldn’t find anything sensible with に .
For what I would have wanted to say in Japanese if I could get the thoughts to properly form in my head: If you are feeling ill, I hope you get well soon! If you just meant that you were low on energy, I hope you get some proper rest! Take care of yourself! (Though of course that message goes for if you are ill, too. )
As for what I actually posted in Japanese:
Perhaps it’s best if I actually include an intended meaning? I’m not sure what the etiquette is!
Intended meaning:
“I’d love to respond in Japanese but translating my thoughts from English to Japanese is very difficult for me. Of course, I don’t want to translate (implied: so much as have the thoughts happen naturally), but it’s a bit early for that, isn’t it? Well, that’s okay. These sentences will suffice for today.”
The things I’m least sure about in how I phrased it:
I always worry I sound very stilted. For the time being, I’m trying to use mostly formal speech, but I don’t know if I just also sound really stiff and unnatural with my word choices, or if I’m just worrying about sounding stilted because it isn’t casual speech (which I have more practice input-wise thanks to what I read; hence why I figured I’d start with practicing output with more formal phrasings… I need to get that practice somewhere)
Is the location of that ちゃんと (just before the 英語) the proper (hah) place to put that? I almost feel like I should have put it in front of the 訳するの, but I don’t know for sure.
On that note, verbs being turned into nouns are something I’m not confident in. Did I do it right?
I bolded the second 訳す usage, because I wanted to emphasize that I don’t want to translate the thoughts so much as just have them, but I’m not really sure how I would express that nuance in Japanese. Even the way I phrased it in English sounds weird in my brain, but I think I’ve just spent too long thinking about this. Hopefully that indirect question makes sense.
Finally, is 足りる or 間に合う a better use for “to suffice/to be sufficient” in this instance, you think? I wavered back and forth, and decided 足りる felt more natural, but I’m going purely by gut feeling on that one. I also floated 事足りる in my head, but I’m honestly at a loss which would be the best one.
Thank you for the feedback! 
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