I'm working on a story about a (West at the time) German born mother and her son. The story takes place circa 1999 and by then the MC's mother has been in the US for about 15 years. I wondered how well she would retain her German fluency if she only visits Germany for a few months out of the year every few years, but keeps up correspondence with German friends still living in Germany?
Another thing I also wondered too: Some people say that someone born in a given country will, when they're angry/exasperated enough, will still swear/make frustrated exclamations in their first language. I wondered if, given the situation above, the MC's mother would do so, or swear/exclaim in English instead?
Edited to add: She would have been in her late 20s when she left Germany in the mid-1980s, if that helps/influences any answers. She would have been born in the mid-50s, and while she originally learned English to teach it in Germany, I was thinking that after she gets to the US she may work as a German teacher in an American school. After reading some answers, I'm tempted to make it so she swears in English, but, as a couple people pointed out, might revert back to using German numbers and such when under duress. I'm trying to make sure this sounds realistic enough given this background. Thanks for all the help so far!
Edit 2: I think I've got a good idea on where to go now, thanks!
Research: Googled 'parent swears in native language,' and 'retaining native fluency in foreign country.'