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Hi Miky,
I would like to inform you that the express courier has just picked up your shipment. You should receive it in two or three days.
Please see the delivery note enclosed (or the delivery note attached).
Please excuse our delay in replying to you. We have been busy moving our warehouse to a new building and have had some problems with our internet connection.
Can you please advise if you need any other goods for next week? Our company is closed for 10 days during the August holidays, but if you send your order quickly we should be able to arrange delivery prior to our closing date.

Yeah as Michael says both are correct. In a way the first one asks "How long has it been since you started and then continued to study German?" while the second one asks "How long have you studied German for up until this point in time". So it is two ways of asking the same thing.

It depends on what you are talking about. Let's say you held something that was acting weird (like a clock that would stop and start) you would say "This is being weird" describing the clock. Another example would be "The weather is being weird". Saying "This is weird" would normally describe something weird that did not involve an action (if it looked or felt weird or a weird event occurred). The word "really" in this case is an adjective that is used in the same way as "very". So you would normally say "This is being really weird" or "This is really weird". The other question you had would make sense if you said "I am interested in American movies". It means you are currently interested in them in the present tense. Hope this helps!