Caps Lock
Most people in Poland use the Polish programmer's layout: a normal QWERTY where the Polish letters are typed with the right Alt key (AltGr). AltGr + A gives ą, AltGr + L gives ł, AltGr + S gives ś, and so on, with AltGr + X for ź and AltGr + Z for ż.
Polish letters are frequent, and reaching for AltGr without looking is the main skill to learn. The hint under the text shows when AltGr is needed and which finger to use.