If the list of books looks too long, please leave out the foreign books.
Literal
Book [attributive-の] list [subject-が] too-long seems-[if-だったら], foreign [attributive-の] books [topic-は] omit-[please-てください].
Several layered patterns. ~すぎる ('too much') attached to 長い → 長すぎる. ようだ ('seems') + だったら (the たら conditional of だ) → ようだったら ('if it seems'). 省く ('to omit, leave out, exclude') is a native verb for removal from a list or set. リスト is a katakana English loanword.