The word for thank you is matondo or botondi. jcfeser seems to be more familiar with things in East Africa than it is with Central or West Africa. Just because it has not learned much detail about Lingala it says Lingala is simplistic. Really though it is its knowledge of Lingala that is simplistic. If it would learn more about Lingala it would be better able to represent it accurately.
Lingala is easy to learn in a way similar to how Esperanto is easy to learn. When a language is realized to serve the need to allow a large number of people comming from different language backgrounds to communicate efficiently the language is going to be easy to learn. Contrastingly, when a language is realized over many generations to serve the need of a single integrated people all from the same social background to communicate just amongst themselves, it can be much more full of complex modes of expression and can be harder to learn. Still though, speakers of Lingala are just as inspired and inventive as speakers of any other language, so they have taken Lingala as a language and adapted it to fully allow communication of all the usual categories of human expression, covering all the range from high society to low society. Whatever a human might want to express in any other language, it can be expressed in Lingala just as well. There are versions of Lingala that don't use much French vocabulary, but they can still be used to speak about whatever topic. People in Kinshasa-Brazzaville speak Lingala with much more French vocabulary and French code-switching because they are more comfortable with it, after having absorbed a lot of French in their education and media.