帰国まで100日切ったって英語でなんて言うの？

There are less than 100 days until I go home. (You could replace home with "on vacation," "to Japan," etc.) "Less than," tells your listener that you are under 100 days until the event. Maybe you have 99 or 67 days, but the days are fewer than 100. "In less than 100 days, I return to Japan." (Return means that where you started, or where you are from, you are going back to that location.)

There are a number of ways to express this. You can also state the exact number of days by saying, for example, "Back in Japan in 83days" or "I have less than 100 days until I am back in Japan.

If you wish to express you are feeling sad about something conversationally or in a message, you may say or write: 'sob, sob'. It is equivalent to the crying or sad emoji.

When posting on social media it's not always what you type but by adding emojis to show how you are feeling it says it better if you 'can't believe' something then you are finding it hard to understand

"Sadly, in less than 100 days I will be going back to Japan.": Starting the sentence with "sadly" shows that it it not something you are happy about. "Unfortunately I will be home in less than 100 days.": Saying "unfortunately" in the beginning of your sentence is a way we can show that we are sad about a certain situation.

Native speakers will say like this: “I'll be returning to Japan in less than 100 days”. There are lots of other ways to say it, but this one is the most accurate and most commonly used. Here is an example on how to use this in a conversation: A: How long are you staying here for? B: Sadly, I have less than 100 days to spend here, before going back to Japan.