Maybe an "ambrosia fruit salad" offering in key-board layout.

QWERTY with the monetary symbols for USA and the UK, and some "Spanish" keys and dead-keys, too... ???
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This is a heck of a work, these keys look magnificent.
Surely this keyboard layout is puzzling. If it was some kind of keyboard for spanish-speaking North-Americans, forgiving the use of the inverted question mark, as the fractions and dollar sign keys would imply,  surely the pound key on shift-5 is puzzling. There is no diaeresis either - this should rule out 'real' Spanish, Portuguese  and Esperanto. Moreover no cedilla or circumflex accent so other  languages using these like Romanian and Turkish are ruled out. Interesting enigma. I happen to have an Olivetti Lettera 22 with Spanich keyboard and it has them all: circumflex accent dead key, tilded N, inverted exclamative and question marks, and so on.  I am still inclined though to think for your 22  to some kind of production for spanish-speaking Americans as today the only Spanish keyboard in use (on computers) I know of without tilde and cedilla is the 'Latin-American' (that has no tilde -  but HAS  a 'tilded-N' key. The fractions imply some  use of the  Imperial metric system in my opinion, thus my hypothesis points to some North-American Spanish-speaking large community with the need to often write in English as well. 

I do not  know exactly what it took, back then, to order an "unusual" Olivetti (math, French or German or English..) but surely it took a lot of time as there are some  loitering around in Italy  but those mostly  appear  to have been taken back home from nearby foreign countries or bought in non-Italian speaking areas in Italy (like Alto-Adige/ Tirol). There you can find most Olympias and Hermes on sale in Italy, and surprise surprise many have QWERTZ keyboards.
Also, I noticed most 'English' QWERTY machines offered for sale are from south of Italy and Naples in particular (areas with a high proportion of  inhabitants that worked in the USA or, in Naples, worked there with North-Americans or are American themselves, think sixth-fleet suppliers and the like) so mostly not ordered from Olivetti as such, even if they are Olivetti machines. Surely ordering an ad-hoc machine in Italy was difficult.
But what people could find sloow or too expensive, importers and manufacturers could have turned into perspective sales. Olivetti had a strong presence in 'foreign' markets in general and the USA in particular, that absorbed most of its more exotic and expensive products, mind goes to the Programma 101  that have been sold mostly in the USA.   Given the fact that areas with a relevant number of spanish-speaking people  in the USA are diverse, some rich and enormous (think Florida, Texas, Southern  California just for a start)  maybe a demand showed itself.  The presence of the £  (pound) character could be explained by the practical need to avoid casting  new typefaces and to avoid changing keys positions on the keyboard, and also to avoid having the same character appear twice (thus the pound on the Shift-5  was carried over from one  already available key on a possible valid position).      

Good points duna and M. Höhne, thanks!