If you differentiate between different types of english, it makes sense to show a US flag or UK flag for the different regional variations.
If you have only one version per language, just show the flags side by side. UK/US/AU/NZ for english, DE/AT/CH for German, etc.
On the other hand € stands for 20+ languages and $ means USD, NZD, CAD, many kinds of Peso and many other types of dollar.