On letters

[Anachronist]

This might be a really stupid question, but what languages and letters (which runes) Do the normal people of Esgaroth or Bree or Minis Tirith use, when they write diaries, lettres and other mundane stuff at the end of the third Age?

[Stormcrow]

Bree-folk and Lake-men speak Westron, also known as Common. They speak it differently, but they can understand each other. I don't know what script they use. I would guess that Lake-men can read the dwarf-runes represented by Anglo-Saxon runes, but somehow I don't feel like they'd use those letters for daily writing. They might.

Gondorians speak Sindarin and Westron. I expect they write with the Feanorean letters.

[Stormcrow]

By the way, see pages 35–36 of the rule book (pp. 33–34 of the Adventurer's Guide in the older slipcase edition).

[Otaku-sempai]

You should, if possible, reference LotR, Appendix E: "Writing and Spelling". On writing:

The scripts and letters used in the Third Age were all ultimately of Eldarin origin, and already at that time of great antiquity. They had reached the stage of full alphabetic development, but older modes in which only the consonants were denoted by full letters were still in use.

The alphabets were of two main, and in origin independent, kinds: the Tengwar or Tîw, here translated as 'letters'; and the Certar or Cirth, translated as 'runes'. The Tengwar were devised for writing with brush or pen, and the squared forms of inscriptions were in thier case derivative from the written forms. The Certar were devised and mostly used only for scratched or incised inscriptions.

There is much more, but I think that passage answers the main question.