Simredo has a spell checking function. You can see in the screen shot above that the misspelled words 'originaly' and 'begining' are underlined in red. In order to use this feature, you must install a spelling dictionary. Currently, dictionaries for English, Esperanto and Latin are available.

To install spelling dictionaries, click on one or both of the following installation programs. You can start installation immediately (with Open), or save the programs to your disk for later installation.

InstallEngDict.jar - to install the English dictionary, dictionary.zip
InstaluVortaron.jar - to install the Esperanto dictionary, vortaro.zip
InstLex.jar - to install the Latin dictionary, lexicon.zip

The screen shots below show the installation dialogues for English and Esperanto.

The first button is for selecting the installation location. This is the folder where Simredo4.jar and the key map files are located. In Windows, it's probably c:\Program Files\Simredo4, as shown above.

Clicking the Install button starts unpacking the dictionary file in the destination location.

After installing a dictionary, you need to restart Simredo, so that it will recognize that the dictionary exists.

To activate the spell checker, select 'Spell Check' under the 'Other' menu. A dialogue window will give you four choices: Off, English, Esperanto and Latin.

Simredo 4 allows you to add your own words to the spelling dictionaries, although it's a bit complicated. The explanation for adding words to the English dictionary is here. The explanation for adding words to the Esperanto dictionary is here.