orth_chording.py is the main orthographic dictionary.
orth_chording.py is a Python dictionaries and thus requires the plover-python-dictionary plugin to be installed. This plugin can be installed from the Plugin Manager.
By default, this dictionary uses commands from the plover-dict-commands plugin to enter and exit the orthographic dictionary, namely {plover:solo_dict} and {plover:end_solo_dict}. This plugin can also be installed from the Plugin Manager.
When manually defining an entry to enter the orthographic dictionary, you can use {plover:solo_dict} to disable all other dictionaries and enable only the orthographic dictionary. For instance, you can define an entry for {plover:solo_dict:+orth_chording.py} and also include in the command whatever other dictionaries you wish to have available.
The orthographic dictionary should be disabled when not in solo dict mode, since it can generate translations for (essentially) every stroke, which interferes with folding and untranslates.
Exit is handled by a special entry which translates to {plover:end_solo_dict}. By default, the stroke -TSDZ is mapped to this.