any synonym would technically work. i.e terrible, horrible, etc.

it would be better to stick to one language. especially in this case because the sentence structure are so different.

dumplings in mainland. some places call them either gyoza or mandoo which are the japanese and korean versions

Hi there! It (has) been (a long time) [so long also makes sense but seems awkward in my opinion] since I have heard from you. I hope you are doing well and I hope (your family is) doing fine. I am pretty good (despite the) hard work (at) the office. Anyways, the reason I am writing this letter (is) to (inform) you that I have received the photos. (I forgot to thank you and your family) for (the) kind gestures last holiday at your place. I would like to apologize (to) you for not writing (a) letter (since) last vacation. Actually, when (I returned) home after the (trip my boss) sent us (to) London for (a) special training (seminar) for our department. They are planning to launch new programs in our organization. So, we have to learn that program (they will use) in our company. I would like to invite you and your family, next vacation, to my place and it will be my pleasure if you (will) join us. I am praying for (you and your family's welfare) and (wish) you all good luck.

above is correct but the clause can also be used metaphorically. The phrase is used in many conversations and arguments that have no conclusion.

moved & learned.