I have no idea about Estonia, but I am in a similar situation in another non-English speaking country with the end of month deadline
I do not have a tax rep there, so going DIY.
Very little info is available in English in the official sources, and virtually none in the online forums.
I am therefore using Google Translate/Deepl to read the websites and various PDFs.
So far I feel like I am getting there but will only be able to tell for sure after the deadline passes
Most of the official government software you would need to use for this in Estonia will be available in English. That means all the questions will be in English, however some categorisations for some answers could still be in Estonian. You would still need to use a bit of Google translate.