Better dust off my copy of Beowulf to get back to old English. But considering that it is really a kind of German (Saxon), influenced by the Vikings, Latin (Rome did conquer England), and Gaelic, maybe I should just go back to pre-English Welsh or Manx.
The roots of modern English are indeed a north german folk language. Over the centuries the influence of many other tongues has been added, to one extent or another. Viking words are fairly common (their, them, skin for example) but Gaelic is surprisingly scant (apart from place names). The Romans did NOT conquer England, as there was no such country when they were in Britain, consequently there is little latin influence from that time. Most Latin words in English were picked up in the middle ages, when Latin was the language of the Law and the church.
The biggest single influence on English (some 20,000 words) is actually French, from the time of the Norman Conquest. They tend to be legal (e.g. justice, jury, accuse, acquit, treason) or dealing with ruling (court, parliament, government are all french words) Also military (e.g. mercenary, battle, fortification) or culinary (mackeral, market, mutton, beef, fruit).