Why is someone on the airplane giving me strange looks if I'm speaking fluent German?

I'm from Germany and I speak fluent German. German is my first language. I struggle with pronouncing a lot of words in English so it's easier for me to just speak in German. Thus I speak in German every day. Yesterday I got a whole bunch of weird looks when I uttered things like Flugzeug, Flughafen, Himmel, Haufen, Wolken, and phrases like "Wann ist dies Flugzeug gehen zu landen?" "Ich liebe nicht dies Gewitter. Es okkuriert zu uns zur�ck in 2007 auf das Weg Heim und wir fast gestorben." I don't get why people look at me like I'm an idiot. I can only spell in English but pronouncing everything is hard. I write the same but I just speak differently. I also speak to children on the plane who also speak in the same language.