Language is important for cultural as well as for economic reasons.
Within a community, it is important that there be a common language that everybody can communicate. In China, it is Mandarin. In India, it appears to be Hindi and English, though there are many other languages in use. In Malaysia, it is Malay. In this situation, language defines the culture and influences it. It is always lovely to listen to locals speaking their own variant of the language. The variety makes for cultural richness.
For economic purposes, it is important to be conversant with the trading language. Within the local economy, it is Malay. Within the global economy, English is the dominant language for commerce, as Spanish and Portugese were in the olden days. In the last few decades, Japanese was thought to be important. Now, Mandarin seems indispensible.
In the field of learning, especially Mathematics and Science, the current contention is that English is the proper medium of instruction. This objective kills two birds with one stone - to enhance the use of English and to enhance the learning of Mathematics and Science - which implies the availability of super-teachers who are good in all three subjects. The idea behind this may be to create an elite scientific class of students who could compete in the international arena.
This idea is not flawless: (i) The Chinese schools have always claimed supremacy in the teaching of Mathematics in Mandarin. (ii) It may be hard enough to get ordinary school children to master their Mathematics and Sciences in their own languages, without adding the burden of learning the English. (iii) Teachers may not be up to the composite task of teaching English, Mathematics and Science at the same time.
At the end of the day, knowledge in multiple languages is important for survival in the global economy. Proficiency in Malay (for culture) and English (for economic survival) is important. Some may wish to add Mandarin or Tamil or Hindi to the arsenal of modern-day survival kit, but as supplementary. While Malaysia is unique in that all these three languages are well spoken in the country, they are by different segments. For integration, there is a need to strengthen the teaching of languages in schools. The education system may take a Malay+English+1 language policy, with Malay as the medium of instruction in national schools, English as a compulsory area of study, plus the need to choose an option (Mandarin, Tamil, Japanese, etc.).
This language formula can be applied to the vernacular schools. In Chinese schools, the medium of instruction is Mandarin, with Malay as a compulsory subject, plus an option (English, Tamil, etc). In Tamil schools, the medium of instruction is Tamil, with Malay as a compulsory subject, plus an option (English, Mandarin, etc.).
For Mathematics and Science, the teaching should be in their respective medium of instructions. For Science, maybe the answer is to leave the terminology in English.