В английском у нас есть слова.... , по-русски это ..." "In English we have ..." is not exactly the same as "I write in English". "по-русски" means "in Russian manner". You can use it to mean "doing things in Russian way" in general. Similarly: "по-моему" ("in my opinion") is "in my way". "на русском" can be used instead of it, without much difference in meaning. 1. When listing several langauges: "in English and Russian" you can say: по-русски и по-китайски на русском и на китайском на русском и китайском. ?по-русски и китайски is questionable 2. you can add "language" to "на русском". на русском языке you can't do this with "по-русски". 3. You can't add по- to those names that are not adjectives. на бурушаски One slight difference in perception is that when hearing Я много читаю по-английски - I think more about the person and his experience with reading English, while when hearing Я много читаю на английском - I think more about text written in it. Maybe the same thing makes you say "speak English" (without "in"). Yet it is acceptable to say even in formal langauge that a book is written "по-английски".