For non-native English speakers, it is only natural to think in their native tongue and use local idioms. When doing any of the IELTS sub-tests, the thinking process takes longer than a native English speaker.
The thinking process for a native English speaker would normally be, think in English and say it in English. Non-native English speaker, would have 2 additional steps; think in the native tongue, translate to English, check grammar and say it in English.
The solution would then be to “think in English”; this of course will take quite a bit of time. I would advice to start with something simple, your daily thoughts about the things around you could be done in English, an example would be commenting on the weather “it’s cold outside”; if you day dream, try day dreaming in English as well. Keeping a journal would be very beneficial, keep in mind to think and write the journal in English.