Haha, at least you know a bit about singapore. But yea, English is our first language. Singlish is Singapore's unofficial first language and it is heavily peppered with local slang. In fact, some of the sentence structures of certain singlish phrases are taken from mandarin or malay, so they may not make much sense from an English perspective. For the older generations especially, some people ONLY know singlish and not proper english because english was not the language of instruction in all schools in the past. They either attended an English medium school, or a mandarin/malay school, or not go to school at all. But for the last few decades, English has been the only language of instruction in all schools (Im not too sure about those people in islamic schools though) but Singlish is as alive as ever due to it being so rampantly used amongst parents and grandparents.
Today, if you visit singapore. You might get quite confused as there has been a recent flood of Chinese immigrants from China. A lot of them hardly speak any English, and they are mostly hired as service staff at shops and eateries, so knowing mandarin would come in real handy. Glad I learnt mandarin as a second language! (tho i struggle when i try to converse with people from china)