Where does “Alemania” (what they call Germany in Spain) come from?

I think the term "The Nethetlands" was coined after the Reformation and Counter-Reformation when the northern provinces ,which became Lutheran, separated from the southern provinces which remained Roman Catholic.

The country was usually referred as "Holland" (a northern province) before then.

There’s no actual difference in meaning/etymology between ‘Diets’ and ‘Deutsch’. They’re both derived from Proto-Germanic *þiudiskaz, meaning ‘of the people’. Well into at least the seventeenth century, probably the eighteenth (I’m basing this off what I’ve read myself in primary sources) ‘Duits’ was still commonly used in the Netherlands as well. It was essentially part of a distiction between ‘Duits’ and ‘Waals’, where those who were ‘Waals’ were the ‘others’.