Since inception, Pakistan has faced issues in various ways. One of them is language. Pakistan has two official languages: Urdu and English. However, this has a severe problem attached to it.
Historically, When tensions with East Pakistan, modern day Bangladesh, were rising, one of the many reasons for conflict was the language issue. Now, at surface, it may seem that administrative differences led to escalation, however it can be argued that language might have sown the seeds of divide. When Jinnah was asked to include Bengali as one of the official languages of Pakistan, the request was denied. This might have well led into the Eastern wing believing they are being neglected. Eventually after severe conflicts, Bangladesh came into being in 1971.
Language carries with it an identity. Most ethnicities have their own language to communicate and represent their group. In Pakistan, these official languages are spoken by a certain amount of people and most, if not all documentation, is done in either Urdu or English. However, Pakistan is not as homogenous as it may seem. It is home to 4 provincial languages, Punjabi, Sindhi, Balochi and Pashto, as well as bordering languages, such as Brohi, Seraiki, or even Hindko. But these are only the ones that are relatively heard of; the country harbors well over 50 languages spoken. To think such a diverse country has language issues is ironic.
The issue that occurs due to neglect of language is ethnic divide. Now, this may seem like a generalization, but this is true. Nevertheless, how does language lead to divide? The answer is not as simple, however I will explain it as much as possible.
One of the issues that arises from language is representation. If a certain ethnic group's language is disregarded, it leads to the impression that the group is being marginalized. Now, it is important to consider population size does not define marginalization; it occurs whenever a group is being targeted or ignored. When language is not factored, it results in a lack of political concern for an ethnicity, leading them to feel helpless.
Another issue that occurs is with education. Recently, Pakistan decided that a Single National Curriculum will be implemented, with the medium of instruction being the official languages. While it may seem like a beneficial, uniting move, it is in fact the opposite. What about children that cannot understand these languages? What happens to their education? Not only does this put other ethnic groups at a disadvantage, but it also forces them to learn another language, which may be difficult to do so.
However, there is hope. If teaching occurs in local, or even provincial languages with the option of studying in one of the official languages of Pakistan, perhaps it may lead to students gaining confidence in the system and learning to the best of their abilities. Presently, however, this is a tedious task that requires a lot of effort, and perhaps even then it may not be implemented completely. Lets see what the future holds.
The issues, that you identified, associated with language and factually and historically correct. Giving preference to one language over the other does create ethnic divide. It even gets so worse that one language is constantly shown to be dominant over the other. The dominance of Punjabi and Punjabi speaking folks in the politics of Pakistan is just one clear example.
Yes, the provincial government must prefer local language as the teaching medium for all government and private schools. One could say that there are issue with this policy that what those students who lives in Baluchistan and study in Punjab if the teaching medium is converted to Punjabi, and the student from Baluchistan cannot understand Punjabi language? Well the answer would make different sections for different ethnic students after all there are 4 to 5 sections for each class in each school. So, it would be great if the teaching medium will be used according to certain local cities because it will enhance the understanding and creativity of students.
I agree that the teaching must occur in the local languages and I have recently watched an interview of Dr. Mariam Chughtai in which she said that it is up to the provincial government whether they want to implement the Single National Curriculum in the local languages or not. According to the 18th amendment, it is the constitutional right of the provincial governments to decide the curriculum and medium of instruction. I think the provincial governments must use their right and set the local languages as the medium of instruction.
A few days ago our PM Imran Khan said at the launch of SNC, "Mental slavery is worse than physical slaver." He said this by pointing out that we are so obsessed with English language that we have started to adopt their culture. He said SNC will promote our own culture and it will unite us. But, I believe, SNC being in one language will again make people of different language the mental slaves of one dominant language. Hegemony is still there. Diversity is still being ignored...
You have rightfully pointed out the importance of language in ethnic representation. Marginalizing a language within the important spheres of society is synonymous to marginalizing an ethnic identity. Single National curriculum is promoting language hegemony and blatantly dismissing the importance of all regional languages. What it's drafters need to realize is that an ethnically and culturally diverse society as Pakistan would have different education needs. We cannot snub out and ignore our differences under the guise of promoting unity.