"I do not wash my clothes in fall and winter."
I am wondering about this too. One of the other phrases was 服は洗いません, so why is it 秋と冬は服を洗いません here? I had thought that を was used as an object marker for verbs that you were actually doing (like when you are washing your clothes - 服を洗います), but if it's something you're NOT doing, then you use は for emphasis, as in the example 服は洗いません. Is the use of either particle okay?
The basic structure of Japanese sentences is WHO は SOMETHING を ACTION, and if the action was done during the particular period, time, and season whatever, they are mentioned before SOMETHING. So the basic structure is changed like this. WHO は WHEN に SOMETHING を ACTION. OR WHO は WHEN には SOMETHING を ACTION. OR WHO は WHEN は SOMETHING を ACTION.
The sentence with に, this form usually has been using to mention the annual things. For example, 私は秋と冬は服を洗います。 This means the clothes are washed during autumn and winter USUALLY but it does not care that the clothes are washed or not during spring and summer. The sentences with には and は, this forms usually have been usjng to mention a particular things. For example, 私は秋と冬は服を洗います。or 私は秋と冬には服を洗います。 These means during the autumn and the winter, the clothes are washed, but during spring and summer, the clothes might be not washed or be washed. These forms are used for positive and negative sentences. In this case, the answers should be answered with following form. 私は秋と冬は服を洗いません, or 私は秋と冬には服を洗いません。
I would have said that same thing. But i think the point here is that the most important information in this sentence is not that they don't wash their clothes, but specifically not in Fall/winter. So, that's the topic, so you mark that with wo. I personally wouldn't create a sentence like this. But it's not technically wrong. I would have said 秋と冬には服を洗っていません。
I assume you think は is a subject marker?
は is just a particle that marks context, it can sometimes marks what you are calling a subject but is not always the case. When you see 〇〇は、this is not important for the meaning, the thing marked by は is only there to let the listener know what we are talking about it, most of the time this is omitted because is understood by context. 〇〇は is important for context. は can sometimes marks the
So you could say in this regards that the sentence has 2 parts「秋と冬は」「服を洗いません」"speaking of fall and winter, I don't wash clothes (around that time of the year)", where the first half of the sentence is there just for context and has less importance to the meaning, while the second part is the meat of what the speaker is trying to say.
You could use に as well to mark 秋と冬に、this marks the time as more specific and most probably will change the meaning of the sentence from a habit you are describing (not washing clothes in those seasons) to a decision like "I will not wash my clothes in fall and winter", but since we are only just describing what we do in those seasons and not other ones, the は particle does the perfect job.
You could also phrase it with は marking the "doer" of the sentence (sometimes called "subject" in English resources) like「私は秋と冬に服を洗いません」But I'm pretty sure this sounds less natural, you don't always need to include 私 in a sentence, is understood if the words are coming out of your mouth already.
If you wanted to be more specific while sounding natural you could also use が which is the "doer/be-er" marking particle, this is the equivalent to the subject in english, but since this is not expected, it creates a strong emphasis that is "you" who does this action.「秋と冬は私が服を洗いません」"it is me who doesn't wash clothes in fall and winter".
This is not just a "strange" Duo thing. Definitely true for some people here in Japan. You can tell when you're on the trains. One explanation I got from a Japanese co-worker was that "the clothes would freeze when you hang them out to dry." I kid you not. I suppose that might be true way up north, but my clothes certainly dry outside just fine all winter in Tokyo.