Vocabulary is correct. “Vocabularies” would be used only in unusual situations, for example talking about multiple persons’ vocabularies (“my children’s vocabularies are increasing every month”) or one person’s vocabularies in more than one language (“my English and Chinese vocabularies are both much better than my Spanish vocabulary”). You would not use the plural form to talk about one person and one language.

Its helpful!

Yes and also you can read books and watch some TV shows with subtitles in english.