[1] 柏林的邮局很大很漂亮。( very good!)
[2] 今天我去了邮局寄一个包裹了。(the last word "了“ should follow the verb "寄“,今天我去邮局寄了一个包裹)
[3] 我来了邮局得很早。(still the problem of "了”, 我很早来到邮局 or 我来得很早 or 我很早就来了,it's due to which part you emphasize)
[4] 可是邮局人多,用排队!(可是邮局人多,要排队!用vs要 just like "use" vs "need")
[5] 我跟工作人员说: 我要寄这书往德国。(我要把这本书寄到德国 or 我要寄这本书到德国,a little bit complicated to specify...)
[6] 他告诉我:你得填这张表。可是我不回写汉字!(可是我不会写汉字)
[7] 然后我给我的好朋友打电话了,让了他来这儿帮助我。(the first "了“ is acceptable, but the second " 了” is not needed definitely.让他来这儿帮我)