German Bibliothek, French bibliothèque, Italian/Spanish/Portuguese biblioteca, Polish biblioteka, Russian библиотека, ...
Libraries are a Greek thing in many languages. ;)
How would one distinguish a library and a bookshelf?
Or book case?
They mean a slightly different thing but they are used almost interchangeably nowadays, at least according to what I've read.
Yeah but dónde está la biblioteca?
It's ok to include the 'ν' in στην? .. . στην βιβλιοθήκη
According to the official grammar, it's not, but virtually nobody pays attention, so, either is ok.
I thought I read that the 'ν' is dropped in informal speech, but kept in formal writing. And, according to newer grammar rules it should be kept.
It is dropped in both formal and informal speech, unless one is speaking reeeeally slowly. The newer grammar rules concern the masculine definite article only.