"I buy it myself."
Translation:O cumpăr eu însumi.
"Însumi" is a pronoun to strengthen the idea that the subject does the action. In modern Romanian it is out of usage, but you will hear it now and there.
You have two options:
1. Eu însumi o cumpăr. Without the second "eu" when the reinforcement pronoun (Sorry, this is a mot à mot translation from Romanian) is used immediately after the subject.
2. Eu o cumpăr eu însumi. When the reinforcement pronoun is used after the verb, you have to repeat the subject by using again the corresponding subject pronoun.