Since you are mentioning a language selector and specifically if this is some kind of form element, the use of font sizes smaller than 16px is known to cause a for some users rather annoying "zoom effect" worth taking into consideration.
I don't know if this phenomenon has a name other than "zoom effect" but a simple google search gives us this short article from css-tricks discussing just this.
LearnUi.design (which I never heard of before) is the second search result and they mention this as a potential problem since it causes obscurance of parts of the screen.
I haven't really researched this matter, more stumbled over it during my own web projects. I'm sure there are actual studies of this if you have access to large document databases. But only googling it will bring lot's of results.