Guys bon giorno.
I need some help with this.
I have an investor, who is interested in buying a hotel.
This investor wrote me a letter, which includes all the details about the desirous specifications of the hotel (e.g. location, number of rooms).
In English this letter I called it: "letter of interest". It is not a proposal, it is just a letter that includes the demands of the investor. If you check it in internet letter of interest is something different.
But I think in English is a pretty good translation given that it captures the idea. I think so! If you have some alternatives please send them to me. How about: "Specifications Letter" or "Letter of Demands"
How about in Russian?