Should I write my master's thesis in English, as a non-native speaker?
The reasons I write all my work in English, regardless of the country in which I work, are threefold:
- The scientific community works in English
- English texts are easier to reuse
- English texts are easier to share and diffuse
Reasons 2 and 3 are effectively based on premise number 1. In terms of the ability to reuse my work, more often than never I might have to give a presentation, a talk or create a poster based on some report/thesis/paper I previously wrote. This scenario is common to both academia and industry. When this happens I can easily extract sentences, keywords and figures from my previous work if all the text contained in them is in English, without the need to translate it.
Similarly a document written in English can be given to anyone and they'll be able to read and understand it without requiring a translation.
Therefore if I were you I would write the thesis in English, and present it also in English. I don't think that your examiners will feel in any way threatened by this. Ever more so if you are a foreign student and Italian is not your native language. You should not be expected or forced to write and/or present in a language you are not that familiar with, if English is an allowed option.
When you said "none of my professors are native English speakers", did you mean that they have difficulty understanding and communicating in English? The fact that someone's native language is different from English in no way implies their inability to communicate in English fluently enough.
If your professors indeed have difficulty understanding and communicating in English, then it would IMHO be impolite and, even, unethical to choose English as the language of your thesis, thus, making your decision an easy one.
On the other hand, if your professors can communicate in English with enough fluency (and will heave no problems understanding your subject domain terminology), then I think that producing a thesis in English would be preferred. The rationale is that your thesis can be shared with (and understood by) much more people and, while you might not see value of that today, perhaps, tomorrow you opinion will be different. Sharing your thesis with more people might be beneficial from two perspectives: academic (disseminating research) and professional / non-academic career (communicating your professional knowledge, skills and abilities to potential employers).
It seems likely to me that your professors would have no difficulty reading your thesis in English and even understanding your presentation in English. They might, however, feel uncomfortable asking questions or making comments in English. If that's the situation, then you might consider doing your writing and your presentation in English but making it clear to the professors that you are willing to take questions or comments in Italian.