Glossary should be as small as possible while including all the things that need explanation or consistent translation. It's for 'terms': words or word combinations that have specific meaning, beg for an explanation and/or are important to be translated consistently throughout the text.
In games, that means we add all world-related stuff: factions, troops, buildings, etc., even if they're pretty standard, like 'farm'.
Glossary shouldn't include whole phrases or sentences: it's translation memory's job.
Include all game-specific terms, especially if they need explanation
Include all non-standard UI strings
E.g., there's no need to include things like 'Ok' or 'Cancel' unless we see actual problems with consistency from the fans
When in doubt, include it, mark it, and we can later prune the glossary if needed
Write terms as they would be written in the middle of the sentence
E.g., capitalize only if it should be capitalized everywhere, otherwise start with a lowercase letter
This helps people understand if the term should be capitalized (even though they'll follow their language rules)
Write terms in their original form
E.g., for nouns, it's singular, nominative case, unless it's a noun that's always plural
Specify part of speech if it's even slightly hard to tell from the word itself
E.g., if you have a term 'lock', specify if it's a verb or a noun, and please always mark proper nouns
Add definition and any relevant information to the description but keep it short
