If you do not have a Latin spellchecker installed, when you upgrade to a new version of LatinEdit, it will ask you if you want to install one. If you choose not to, you can always install it later by choosing Install Spellchecker from the Help menu.
The Spellchecker consists of two files la.dic and la.aff, which are placed at ~/Library/Spelling/ The licence agreement is also placed in this folder.
This is a Hunspell dictionary, written by Karl Zeiler who adapted from Jean-Pierre Sutto's version of mlatinoo. The original files are available on Github. Once installed it is available for all programs.
In LatinEdit, the Latin dictionary will automatically be selected if you click on a Latin field, and the Automatic dictionary if you click on the English field.