I just wanted to add a few more things. I urgently need to express them.

1) We keep emailing each other (two people involved) in English because we both agreed to use English as the lingua franca.
2) Therefore, we must vary the application module; otherwise, both our students and teachers won't be able to join in and therefore our school's principal won't sign your application for a Comenius partnership.
3) After investing so much time in the project, I really hope you won't go back on your promise. (our agreements??)
4) Let me know about it this evening because our head science teacher had been devoting time to the project, too

1) We keep emailing each other in English because we both agreed to use English as the lingua franca.

2) Therefore, we must vary the application module; otherwise, both our students and teachers won't be able to join in, and our school's principal won't sign your application for a Comenius partnership.

3) After investing so much time on this project, I really hope you won't go back on your agreement.

4) Let me know about it this evening because our head science teacher has been devoting time to the project, too.
I'm not sure of the connection between needing to know "this evening" and the fact that the head sci teacher has been working on this. Should these ideas be put in different sentences, and then one idea put in a different place in the message?

Understood. It seems like you have a few urgent points to express. Here's how you can address each of them:

1) If you need to communicate with someone via email in English, make sure to clearly state your agreement to use English as the common language for communication. This will ensure that both parties are on the same page and understand the language being used.

2) It's important to vary the application module, or teaching approach, to cater to both the students and teachers involved. By doing so, everyone will be able to actively participate in the project. This is crucial for getting your school's principal to sign your application for a Comenius partnership.

3) Express your hope that the other party will not break their promise or go back on their agreements. After investing a significant amount of time in the project, it's natural to expect commitment from all parties involved.

4) Request a prompt response from the other person this evening. Let them know that the head science teacher has also dedicated time to the project, emphasizing the importance of their reply.

By addressing each point directly and clearly, you increase the chances of getting the desired response and resolving any urgent matters.