because I use two laptop computers and 1 tablet every day, I have three NVDA installations. If I've added a new entry to a speech dictionary on one laptop, then I find the easiest way to update the other laptop and tablet's dictionary is to find the relevant .dic file and copy it over to the other computers. Since Dropbox is installed on each of the devices, I paste the .dic file somewhere on DropBox and then copy it into the relevant location on the device.
The dictionary files are in the user folder (I have a shortcut on my desktop to Giles, automatically created by Windows on each device). I go into that and then into the App Data folder, then Roaming, then NVDA and finally the speechDicts folder.
The default dic file is titled default.dic and that is where you will probably have most of your new dictionary entries. Otherwise there is a folder called voiceDicts in which are folders for each synth where you have created a voice dictionary ... I have a folder for SAPI5 in which there are .dic files for Hazel and Zira, and an folder for espeak, which is empty because I've not created any custom dictionaries since I rarely use an espeak voice.
I find it far faster to do the copying and pasting method rather than creating a brand new portable copy just to copy a couple of dictionary files.
I am not certain whether this is necessary, but I also save configuration to make sure the new dictionary files aren't deleted when I shut down NVDA (I have learned better, thanks to advice in this group, not to save settings on exit in case I make a change that proves hard to reverse without sight).