Я часто ошибаюсь, когда говорю по‑русски.

I often make mistakes when I speak Russian.

Breakdown of Я часто ошибаюсь, когда говорю по‑русски.

• я: I
• говорить: to speak
• часто: often
• когда: when

Questions & Answers about Я часто ошибаюсь, когда говорю по‑русски.

Why does ошибаюсь end with -сь? Can I say я часто ошибаю?

No, you cannot say я часто ошибаю. The verb is ошибаться (imperfective, reflexive), and in the 1st person singular it becomes я ошибаюсь.

• 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.).