Loosing mother tongue?

"那个方法比较 efficient"
when I should have said 那个方法比较有效率

I would have spit that out easily in my daily life. While Malaysians would considered that a norm, I find that such occasions are threatening my Chinese. I'm sure it won't go to the extent that I can't read or write Chinese but these days, I can hardly sentence my thoughts 100% in Chinese. It has to be topped with English or at times Malay. My TOK knowledge would have tell me that at times, this is what you call the lost of words or meanings during the translation of language. But as I come to realise that I experience none of such case with English, I can only jump to one conclusion, my mother tongue is slowly be replaced with English. On one side, it's better to converse more in English these days but loosing my mother tongue? And I'm heading UK soon. Should I start taking up mandarin classes?