How would you counter someone that says something false, such as, "You don't speak Russian," then you say, "I do speak Russian!"? But how do you emphasize the do part?
There's no such thing like "do" as an auxiliary verb in Russian, thus, there's not such thing like direct analog. But here's a list of phrases than more or less convey the same as the "I do" construction:
- (colloquial) А вот и [нет,] говорю!
- (even more colloquial, even childish) - Очень даже и говорю!
- (more neutral) Да нет, [почему], говорю. (The same "отчего же, говорю")
- (bookish) Напротив, говорю.
- (even more bookish) Отнюдь, говорю.
This kind of "do" is not indicated in the text. All possible variants are either bookish or colloquial. An exact equivalent is emphasized by intonation.
- Вы не говорите по-русски.
- Я́ говорю. (default is "Я говорю́").
Additional words, such as "-то" in "я-то говорю" instead of the intonation change indicates the intention of the speaker to argue. Only the intonation change is as plain and simple, as "do".