In conversations and other situations where you need to be able to process information quickly and respond immediately, translating in your head is a big problem. It slows you down. It makes you hesitate. At times you’ll completely miss out on the conversation because your chance to jump in has come and gone and you’re still trying to translate. On top of all that, a lot of slang, idioms and phrasal verbs can be difficult to translate quickly. If at all! It’s really best for your fluency if you stop translating in your head and learn to start thinking in English.