The Terminology and Wording section of Apple's macOS Human Interface Guidelines serves as a superb starting point for anyone focused on writing clear, helpful content in user interfaces (UIs).
Text is prevalent throughout the macOS interface for such things as button names, menu labels, dialog messages, and help tags. Using text consistently and clearly is a critical component of UI design.
In the same way that it’s best to work with a professional graphical designer on the icons and images in your app, it’s best to work with a professional writer on your app’s user-visible text. A skilled writer can help you develop a style of expression that reflects your app’s design, and can apply that style consistently throughout your app.
For guidance on Apple-specific terminology, the writer should refer to the Apple Style Guide. That document covers style and usage issues, and is the key reference for how Apple uses language.
For issues that aren’t covered in the Apple Style Guide, Apple recommends three other works: The American Heritage Dictionary, The Chicago Manual of Style, and Words Into Type. When these books give conflicting rules, The Chicago Manual of Style takes precedence for questions of usage and The American Heritage Dictionary for questions of spelling.