I'm seeking for a book which contains several fragments of the medieval philosophical works, literally translates them and explains the obscure points for who wants to improve his Latin.
The following book is a good start. It doesn't have literal translations, but it does provide a lot of vocabulary and grammatical guidance.
Reading Medieval Latin by Keith Sidwell
From the blurb:
"Reading Medieval Latin is an introduction to medieval Latin in its cultural and historical context and is designed to serve the needs of students who have completed the learning of basic classical Latin morphology and syntax. (Users of Reading Latin will find that it follows on after the end of section 5 of that course.) It is an anthology, organised chronologically and thematically in four parts. Each part is divided into chapters with introductory material, texts, and commentaries which give help with syntax, sentence-structure, and background. There are brief sections on medieval orthography and grammar, together with a vocabulary which includes words (or meanings) not found in standard classical dictionaries. The texts chosen cover areas of interest to students of medieval history, philosophy, theology, and literature."