French in English
There is no doubt that today English is one of the most important and richest of the world's languages.
Probably the most significant factor accounting for the latter quality was the Conquest of England by the Normans more than 900 years ago.
The conquering Normans spoke French. Most of the inhabitants of the conquered nation spoke varieties of Anglo-Saxon of Germanic origin.
Of course, the Normans were stronger than the local inhabitants politically and naturally their language became the language of the King's court.
It also became the language for written documents, together with Latin, and was generally regarded as "more literary" and somehow "better" than the language of the common people.
In spite of apparently being "worse", however, the language of the ordinary inhabitants of England, and especially the language spoken by the inhabitants of the central part of the country, did not die out.
For centuries, the two languages continued to exist side by side.
Besides this invasion French has influenced English in several others ways.
First, France had its renaissance earlier than England and was a wealthier country than England for many centuries, so England borrowed many words and phrases for cooking, fashion, and arts from France.
Second, French became the official language of diplomacy, so that many words and phrases for law, war, and travel came into English.