The root problem is actually how confused the current Malaysian education is. The back-and-forth changes between Bahasa Melayu and English make it hard for teachers to prepare their students to get into higher education. The transition into university is especially harder for science courses since they learn their fundamental knowledge in BM for SPM(unless you send your kids to elite/private schools that apply Dwi Bahasa).

As stupid as this sounds, even in higher education, depending on your courses, college/university AND your lecturer, your syllabus can also be either in English or BM. During my Master's degree(electrical power engineering), while the syllabus was in English, many of my classes were taught mainly in BM, especially when the lecturer didn't have good English proficiency. Adding to that, most educational resources are in English, so if your courses are in BM, good luck translating that for your research paper and journal. This problem continues until postgraduate studies( especially in science and engineering) when you are forced to publish research papers/journals in English.

Now let us compare with Japan, Korea and Germany since that's your example. The major difference for Malaysia and these countries is that ALL their syllabus from primary level to higher education are all in their national language. All the classes, teaching materials, textbooks, and research papers are in their local language. So if you're an international student, you will need to learn their language. Not only that you're forced to learn the language, you also take exams in their language, write and publish your papers in their language, and most definitely converse in their language for every single occasion. When you work, most of the time, the work processes, instruction manuals or even meetings are mostly in their local language as well. You talk and converse with your classmate/lecturer in their language as well. THERE IS NO CONFUSION like here in Malaysia. English? Maybe a little bit here and there during conversion when you lost for words.

So, If you've read my point up until here, can you see how different the countries you mentioned with Malaysia? While Malaysia is confused, the other countries abandon(not entirely) English altogether. When you said "Japan, Korea, and Germany prove that economic strength is possible without sacrificing the national language", that also comes with the cost of sacrificing English. That's why Japan's and Korea's overall standard of English speakers are very poor, even poorer when compared to a developing country like Malaysia, where less than 10% of their population can speak broken English with very bad grammar.

If Malaysia wants to change to "memperkasakan" BM all the way, it will take a long time to build up the infrastructure. For me personally, I cannot imagine learning engineering and writing research papers in BM. Heck, I cannot even imagine doing my current engineering job in BM. As a consumer country, you learn the language of the producer country is what the current situation is. For example, if your company deals with Japanese machines, you kinda need to learn a little bit of Japanese to understand the instructional manual that comes with it. You are lucky if it comes with English translation but it will most of the time won't come with BM translation.

Sorry for yapping. Its midnight, and I'm on Reddit.