Old English (up to about 1200) has an exclusively Germanic vocabulary, complex declension systems, a completely separate set of pronouns for two people as opposed to one or three, and odd syntax....
The Celtics brought an early Germanic type of language to England. Enter the Romans and Latin. So Latin had some influence on the Celtic languages. The Anglo Saxons entered England next & this...
Modern English is the language that Shakespeare wrote in, and is not very different from our English. However, Old English is the language of Beowulf, and is very different from our English.