Reported for: WPML Multilingual CMS 4.5.8
Overview of the issue
If you create a custom language with an uppercase language code (e.g. aa_AA, be_EN…), you will notice it is not possible to translate the label category from WPML → Taxonomy translation → Categories. Furthermore, the browser console will display this error:
Uncaught TypeError: Cannot read properties of undefined (reading ‘flag’)
As a temporary workaround you can go to WPML → String Translation and directly translate the administrative label of the term.