>> I suppose it depends on your meaning of "new"
Yes, I consider 21 years of age to be relatively 'new' in terms of an idiom, but you are right, that is subjective to an extent I suppose. However, my point is; should a relatively 'new' idiom be used in a message to convey important information to all staff? Particularly when one considers that the insertion of it renders the sentence somewhat incoherent and disjointed.
Ideally, I'm sure idioms etc shouldn't be used to convey information, but they are!
>>Whilst I agree that "Michael won't be in the office today as he has a migraine" is true, it does not convey the fact that he telephoned the office during the morning to explain that he couldn't come to work because he was ill.
"Michael won't be in the office today as he has a migraine" wasn't my sentence, AND you don't know it is true. We are getting in to the realms of philosophy there, so I will leave that there.
OK, your sentence was "'Michael Taylor will not be in this office today due to having a migraine headache" - I couldn't get back to your original post while I was typing my post, but what I typed from memory doesn't differ significantly.
I agree, I don't think that the fact that he called by telephone is relevant in the information to be conveyed, particularly since the fact that 'has called in' seems to be troubling in the structure and coherence of the sentence.
>>In my opinion, it is none of the bosses' nor the other employees' business what is wrong with him, and he can just be described as "sick".
I agree that the nature of the illness need not necessarily be specified in that particular message. However, I'm unhappy with describing someone as simply "sick"; I am much happier using the less ambiguous term 'ill'. However, I'm not saying it should not be used, I just think it is not the best word to use.
How is "ill" less ambiguous than "sick"? I would say that "I'm ill" is used more in BrE, and "I'm sick" more in AmE but, unless we are talking about alternative meanings of "sick" (ie twisted), they both mean "I'm not well"!
>>If I wake up with a terrible migraine and complain to my partner that I feel too sick to go to work, I am not likely to say "I am going to telephone my office to advise them that I cannot come to work today due to my migraine". I would say "I'm going to call in/phone in/ring in sick". I would expect the person I speak to at my office to use the same terminology. He/she would go to the boss and say "Ems just rang in sick, but hopefully she'll be back tomorrow".
I'm sorry, but with all due respect, after reading that paragraph, I feel you have missed the entire purpose and point of my post...especially with that last sentence! The terminology you use and that others appear to understand does not make for the best and correct communication. Think of it like this; If a foreign person had to literally translate the message and as a result is that it made no sense, would that really be a satisfactory outcome? Whilst I concede that using this particular example is a touch pedantic, the fact remains that this tendency and modern trend to 'abuse' the English language with bad grammar, slang and general misuse of words can only results in unsophisticated communication and ultimately communication failure, which is a much bigger issue than people may realise. See 'Abolition of Man; by CS Lewis.
I don't believe that I have missed the point of the thread or your post. Apart from that one slightly misremembered quote, I did not quote your post because I wasn't specifically commenting on it. I was commenting on the entire subject. If a non-native speaker goes to work in an English-speaking company, then they are going to be subjected to what you called "bad grammar, slang and general misuse of words" on a daily basis, probably several times a day.
So many commonly used phrases don't translate directly from English to any other language, but that won't stop them being used nor should it stop us advising learners of the meaning and usage.