is escalation the only solution

You did not mention the language of email you use. I assumed your email language is English and Organizational culture is same as Native culture which is supposed to be. And based on that I express my opinion as follows.

You might change the language (use Native) of your email and most importantly you change the Greetings pattern (salutation and closing of letter) of your email based on their culture.

I guess, the culture is not to read email but to read email in their own language. Reason might be they are not proficient in English or they love too much their native language and consider their culture is highly rich (so far greetings are concern).

Not to read Email is nothing to do with culture, it needs proficiency in language written the mail, love / fun to read and write in that particular language, pleasure feeling with salutation and closing and top of all appetite of knowledge.
You can talk about Ownership / Realization of benefits but those are basic practice of all cultures. They know all those things and practice in their personal and professional life.

However, you can think about trainings on language proficiency, sense of Ownership (Responsibility), Holistic (tangible & intangible) benefits realization, email etiquette, etc. for your stakeholders

Every culture develops based on so much reading and writing in its native language (on paper in past and electronic mode in present), otherwise no culture develops. Therefore, we can not say not to read email is culture.

Just follow the strategy of PMI - started disseminating the project management concept translating PMBOK Guide in different language. It is easy to accept by any hardcore culture.

You can do another thing that is auditory announcement, few cultures they prefer regular / periodic auditory announcement because they are familiar with this kind of system from their childhood.
Therefore, you meet with all your stakeholders (top to bottom) and ask them about their preference to languages of email - English / Native and with consensus you implement. You can take help of translator / interpreter if you are not proficient in Native language and culture.
There is no question about escalation because where to escalate, it's organizational culture inculcated to all - top to bottom.

But not reading and not responding are two different things. Yes emails, if long can be confusing when it is not your native language but writing a simple subject line should get people to at least attempt to read the email. If it is unclear then the recipient should respond as such.