Switching the whole keyboard to different national layouts would be a bad idea as many characters are placed otherwise (the French keyboard being the most obvious example). With an LED keyboard, you would be searching where the damned "é" now is, as it is typed differently on French, Spanish and Italian keyboards. With a conventional keyboard, you would be completely lost.
My advice: get a keyboard with additional programmable keys (with relegendable caps) and program each of these to one of the different characters needed in the different languages, leaving the "normal" alphabetic field as it is in your national layout.
As an example, adding the specific French, German, Spanish and Italian characters not present on the (e.g.) US keyboard would require 21 keys, ideally programmable on at least two layers to also produce the upper case characters.
Keyboards with those capabilites are for example the legendary Cherry G80-2100 and its successor G81-8308 (the latter alas with awful MY switches) or
the Tipro keyboards.
An even easier solution would be to stick to the usual keyboard and just add a programmable keypad with relegendable caps.
