If you ever study German, you will find that all nouns are capitalized in German. Something like this:
Various Languages have different Rules for their Grammar, and these Rules can sometimes seem strange to People whose native Language is different from the one being learned. Languages also change over Time, and the Grammar Rules and Conventions of the Past may differ from those customary today.
English is a Germanic language and has a strong common heritage with German, and if you go back in time you may find things that are even more similar to German than they are today (English has tended to simplify things as people have become more relaxed and informal in the use of language).
As others have said, English nouns were often capitalized in the past for emphasis, as a matter of style. Today we only capitalize proper nouns like English. (However, in French, for example, the word english would not be capitalized. Different language, different rules.)