Are we talking about contries with more than one official language, or about what languages were/are spoken in various contries?
All European contries contain lingustic minorities. The official language is usually just the biggest one, and historically it was decided to make it the exclusive administratibe language at about the same time in the 16th c.
Henry VIII made sure English was to be used in the administration of his realm. Too bad for the Welsh, especially as they saw the Tudors as "theirs" ("Tudor" was originally the Welsh "Tewdwr").
The same thing happened when French became the exclusive administrative language of France at about the same time.
In 16th c. France was spoken AT LEAST French, Basque, Catalan, Occitan, Gascon, Lorrainian (German dialect), Italian and Breton. Most of them still are, more or less.
The situation was pretty similar in most other countries at the time.