Change Language OS to Spanish

Im living in the USA and I wanted to buy a laptop with Spanish OS for my
mother who lives in Spain... I have been told by a microsoft person that
Ultimate and Business you can change the language settings back and forth,
but that with Home Premium you get to chose it only once. Even for
pre-installed options.

I have been told so twice, but I am reading through your posts and it is not
clear. I am not decided yet. Any advice?

DO you know anything else about this??

Thank you!