A culture shock is a little more than not liking a place, even if you like it or have the best intention to adapt, there are cues that will leave you stressed.
It is all related to your senses: sound, sight, feel, touch.
You might be French but living some distance away in a different country during all your life is enough to have you being stressed to what you have forgotten.
The sound is one of this “stress”. This does not mean you are stressed but stress here is defined as a cue that produces anxiety. The sound of a different language is one thing. With a fast pace bold type of language you might feel that things are going a lot quicker as with a different slower type of language you will feel stressed that things are going slower or indeed you are taking more time to do things or communicate.
This is probably why in some cultures some words are preserved in their original meaning, because seen as more meaningful. One might even forget the lingua of a language. For instance in France one coming from an anglo-saxon country might find it stressful to hear words like “dégrèvement” but might be more receptive with words like “compliant” because it comes from “comply to”. Stress while facing such a problem of a slow language dragging on thing forever, might become irritating at best.
It is then urgent at the time of rapatriation to have the propper therapist who knows and is specialised in adapting back with the right speech therapy. Should the person faces other type anxiety coming from a trauma for instance it is chief to address the trauma first to give enough room to the stress level coming from rapatriation first.