P-Derathe

Problem: I want to have the flags not resizing automatically

Solution: Resizing the flag is intentional – it is done to keep the default size of newly uploaded flags. If you want to have a different flag size, you just have to manually upload the flag via FTP into the res/flags folder.

Then, while adding a new language or editing an existing one, you need to choose the "Use flag from WPML" option and paste the file name with its extension.

Now, all you have to do is add some additional CSS, changing the width and height of the class and ID:

#lang_sel_list img.iclflag{
width: XX;
height: XX
}

Relevant Documentation: