Hello,
Well, an interesting question. Would you be able to make synchronization of the source column in .csv for English? 
From the 1st post, I can see that your question was about removing the folder with EN translation (values en), and if the project will not have English as a target, this folder will be removed from integration. The system just can’t “skip” translation for 1 language. Well, it can, if you use API or another tool and download only 5/6 languages, and keep 1/6 always skipped.
The best way to be sure about it would be to follow Roman’s suggestion and do the test in a new project. Figma can be copied, repositories can be forked and used for the test as well. 
I’ve gone ahead and activated a Free Trial for your account - it has unlimited branches, integrations, limits, and all the things you might need for the test. Feel free to play around with different setups.
A free trial will automatically expire in 2 weeks and once it does you’re welcome to jump back to the Free plan. Or mention me here and I’ll switch your account from my side 