Currently we use the language preference icon as a languages-switch icon as well (see 'About' menus of just about all KDE software).
The iconography for that purpose isn't too good IMO. From the icon alone I wouldn't be able to tell what the menu entry does.

We also have an action icon 'languages' also known as 'set-languages'. It is only available in sizes 16 and 22 though. Which isn't much better I think. And the fact that it doesn't have higher detail versions is making it not too good for when we render the icon at a larger size and could pack more detail in.

It be grand if maybe we can create a better suited icon for language selection. 

For example the distro-independent installer Calamares also has need of one to indicate that a combobox is for language selection. Since the UI by default may be in english and the user may not speak english the icon needs to speak for the use of the combobox as test cannot aid in explaining the UI here. I am going to attach a screenshot of what this currently looks like.

This also brings me to a suggestion: A go-to icon that is often used across software these days seems to be a kind of book with flipped languages. You can see it in the calamares screenshot. Perhaps a "breezified" interpretation of this would be the way to go?