Both Alt keys may not be the same on some International keyboards!
Most PC Keyboards have an Alt key on either side of the Space Bar. In many countries, either of these keys may be used.
However in some localities, especially those where accented characters are used, pressing the right hand Alt Gr key has the same effect as holding Alt + Ctrl together. It is used to generate a third character from some keys.
For example on the top row of a British English keyboard, shifted 4 generates $ (Dollar Sign), If you hold down the Alt Gr key instead of the shift key and press 4, it will produce a € (Euro Currency Symbol)
In English braille, the Euro symbol is dot 4 plus e.