I want to thank you for a wonderful first semester.
We use the indefinite article to give a description of the impression that we have received personally while studying in the first semester. We consider the first semester as wonderful.
I want to thank you for the wonderful first semester.
In this case, we inform our interlocutor that it is a common ...
These mean different things:
I want to thank you for a wonderful first semester. - a WFS is not especially stressed, just one semester and, perhaps, it's not over yet.
I want to thank you for the wonderful first semester, on the other hand, means that the WFS almost certainly lies in the past and it is that semester, both the speaker and listeners know ...
You can get rid of the "if" (and I'd also use a hyphen, as there are two clearly separate, yet related statements) (and I'd also add the word "really", for emphasis).
I wish I could get my teachers to read that article - that would be really worthwhile.
You could also say:
It would be really worthwhile if I could get my teachers to read that article.
There are a myriad of ways you can think of formulating a sentence. But let me make your first sentence grammatical and succinct.
If only I could get my teachers to read that article; it'd be worthwhile.
A standard turn of phrase (idiomatic usage) for the context here is...
With apologies to Mirza Ghalib...
(Your poetic efforts, which you admit are feeble compared to one of the acknowledged "poetic greats")
This is a common self-deprecating way of admitting that you know your "poetry" isn't particularly good by comparison - but at least you're trying ...
"Does he say goodbye before he left" is wrong as it contains a mixture of tenses, but the meaning in context tag may be significant - the correct version will depend when the question is asked in relation to when "he" left. For example :
"John just left." (past)
"Did he say goodbye before he left?"
"John is leaving soon." (future)
"Does he say ...
It sounds fine to me, and one thing to note is that these things are always difficult to write, as there is generally a concern about being bothersome (which could go against you).
I would probably write something like:
I have yet to be contacted and am wondering if you are able to provide these details.
The way you write it will also often depend on ...
These all depend on the context of course, but I would consider five of the six uses completely standard. I don't think the use of "I feel" or "I'm (I am)" makes any meaningful difference.
The only one I wouldn't consider standard, though in a rather narrow set of circumstances not necessarily incorrect, would be the use of I'm cold = I have a low libido.