yes you are right

着[zháo] 用 在 动词 后，表示 达到 目的 或 有了 结果：打～了。没见～

here you go https://www.baidu.com/s?wd=外国人为什么来中国学习

Hey Joseph , only meaningful part is "说-黑话", the part before dash mark can be altered to anything that carry the same idea , one speaks with mouse full of ink is a good example, but here I guess "谈心" actually can strengthen the idea of "说-黑话" by contrast, because all we know about heart-to-heart talk is associated with qualities like straight, sincerity and honesty. as for 谈心不点灯 is easy to grasp the idea ,visually . "黑话", A--saying north but meaning south B--it's like those words we can get when we google gangster slang,con man slang, doctor slang ,child slang ,regional slang etc.. any obscure and figurative way of talking, code with hidden meaning ... C--it depends on the situation, itself as a word could be showing disapproval D--no better way learning it than Baidu searching '黑话' ,but it is a deep deep rabbit hole. 怎么用它？ it's good to know, but generally we won't use it on any occasion.

海---外--- literally is talking about the overseas land ,people need a boat to cross the sea to set foot on this land here in ancient times, if one are from Tajikistan or Russia,basically the guy can get here by just walk,but if one are from America or Australia he needs a boat. so my take on this one is 海---外---actually put a little bit extra info to the overall context,but insignificant...and they have almost same meaning...both are fine to learn and use. further check 海---内---外 vs 海---外--- 海内外学生 ; 海外学生 海内外人士 ; 海外人士 feel free to ask,and I'd like to help