Learn Hardcore Russian: Я часто ошибаюсь, когда говорю по‑русски. - I often make mistakes when I speak Russian.

ошибаться = to be mistaken / to make mistakes (reflexive verb)
The reflexive ending -ся / -сь is part of the verb; it’s not optional.
After a vowel it appears as -сь (ошибаю + сь → ошибаюсь), after a consonant usually as -ся (он ошибается).

So ошибаю by itself is simply wrong; ошибаться doesn’t exist without the reflexive ending in standard Russian.

What’s the difference between я часто ошибаюсь and я часто делаю ошибки?

They’re close in meaning, but not identical:

Я часто ошибаюсь
Literally “I am often wrong / I often make mistakes.”
Focuses more on your being wrong, your state or behavior in general.
Я часто делаю ошибки
Literally “I often make mistakes.”
Focuses more on individual mistakes as countable things.

In the original sentence:

Я часто ошибаюсь, когда говорю по‑русски.
Sounds very natural, general: “I tend to be wrong / make mistakes when I speak Russian.”

You can also say:

Я часто делаю ошибки, когда говорю по‑русски.
Also correct, a bit more “schoolish,” emphasizing concrete errors (grammar, vocabulary, etc.).

Why is the adverb часто before ошибаюсь? Can I say я ошибаюсь часто?

Both are possible, but the most neutral order is:

Я часто ошибаюсь…

This places часто (often) right before the verb and is the default way to express frequency.

Other options:

Я ошибаюсь часто, когда говорю по‑русски.
Correct, but has a slight emphasis on the result “I make mistakes (and that happens often)”.
Часто я ошибаюсь, когда говорю по‑русски.
Moves часто to the start, giving it extra emphasis: “Often, I make mistakes when I speak Russian.”

So the original word order is the most neutral and common.

Why is there a comma before когда: …ошибаюсь, когда говорю по‑русски?

In Russian, когда introduces a subordinate clause (a “when” clause), so it is normally separated by a comma:

Я часто ошибаюсь, когда говорю по‑русски.
Main clause: Я часто ошибаюсь
Subordinate clause: когда говорю по‑русски

If you switch the order, you still use a comma:

Когда говорю по‑русски, я часто ошибаюсь.

So the comma is required by standard Russian punctuation rules.

Why is there no я in когда говорю по‑русски? Can I say когда я говорю по‑русски?

Both are correct:

когда говорю по‑русски
когда я говорю по‑русски

In Russian, the subject pronoun я can be dropped when it’s clear from the verb ending:

говорю can only be “I speak”, so я is understood.

Adding я:

Когда я говорю по‑русски, я часто ошибаюсь.

is a bit more explicit or emphatic, but not necessarily stronger; both versions sound natural.

Why is говорю used, not something like “am speaking”? Does Russian have a present continuous?

Russian does not have a separate present continuous form like English (I speak vs I am speaking). The same present tense form covers both:

Я говорю = I speak / I am speaking (depending on context).

In this sentence:

Я часто ошибаюсь, когда говорю по‑русски.

The present tense говорю with часто (“often”) clearly means a repeated, habitual situation: “when(ever) I speak Russian.”
There is no need (and no way) to mark “am speaking” separately.

What verb is говорю from, and how is it conjugated?

Говорю is the 1st person singular present of говорить (to speak, to talk):

Infinitive: говори́ть
я говорю́
ты говори́шь
он/она говори́т
мы говори́м
вы говори́те
они говоря́т

Note the stress:

говори́ть (stress on -ить)
говорю́ (stress moves to the last syllable, -ю)

What exactly does по‑русски mean? Why do we use по- here?

По‑русски literally means “in a Russian way / in Russian” and in this context = “in the Russian language.”

The pattern is:

по‑
- adjective base + ‑ски / ‑цки / ‑кому, etc. → adverb of manner, often “in X language”:

Examples (languages):

по‑русски – in Russian
по‑англи́йски – in English
по‑францу́зски – in French
по‑неме́цки – in German

In the sentence, говорю по‑русски = “I speak in Russian.”

What’s the difference between по‑русски and на русском (языке)? Are both correct?

Both are correct, with very similar meaning, but usage is slightly different:

говорю по‑русски
Very natural, everyday, short and idiomatic. Most common choice in speech.
говорю на ру́сском (языке)
Literally “I speak in the Russian language.”
Also correct; a bit more formal or explicit, often used when contrasting languages, or in more careful / official speech.

What you should not say is:

*говорю по‑русскому – this is wrong in standard Russian.

So prefer по‑русски or на русском (языке).

Why is there a hyphen in по‑русски?

Spelling rule: adverbs formed with по‑ + an adjective or pronoun + ‑ому / ‑ему / ‑и / ‑ки / ‑цки are usually written with a hyphen.

Examples:

по‑ру́сски, по‑англи́йски, по‑францу́зски
по‑мо́ему (in my opinion), по‑тво́ему, по‑ихнему (colloquial)

So по‑русски must be written with a hyphen.

Should русски be capitalized in по‑русски?

No, it should be lowercase:

по‑ру́сски

In Russian, names of languages and related adverbs are written with a lowercase letter:

ру́сский язы́к – Russian (language)
по‑ру́сски – in Russian
англи́йский язы́к, по‑англи́йски
неме́цкий язы́к, по‑неме́цки

So capitalizing it (По‑Русски) would be incorrect.

Can I change the order to Когда говорю по‑русски, я часто ошибаюсь?

Yes, perfectly:

Когда говорю по‑русски, я часто ошибаюсь.

This is just as natural as:

Я часто ошибаюсь, когда говорю по‑русски.

The meaning is the same. Beginning with Когда… puts a bit more focus on the condition (“When I speak Russian…”), but both are normal word orders, and the comma is still required.

What is the perfective partner of ошибаться, and how is it different from ошибаюсь?

The perfective verb is ошиби́ться (“to make a mistake / to be mistaken” once, as a completed action).

Compare:

Я часто ошиба́юсь, когда говорю по‑ру́сски.
I often make mistakes / I’m often wrong when I speak Russian.
– Imperfective, repeated / habitual action.
Я одна́жды си́льно ошибся / ошиблась.
I made a big mistake once.
– Perfective, a single completed event.

So in your sentence, because you talk about what happens often, the imperfective ошибаюсь is the correct choice.